About tools for paper modeling

Of course a righteous paper modeller does not really use scissors for cutting. At least I don't. There are those who, just to show that it is possible, use a pair of scissors. Great. I don't. I think A sharp, small knife like a surgical scalpel or an Xacto (or a clone) is mandatory.
But besides a good knife there are loads of other tools one can put to good use with building a paper model. Some of them I already mentioned in the tutorials section, I will add some more here, because not every tool needs a special tutorial.

For rolling paper
Collect tubes and rods. All kinds and sizes. Just make sure they're sturdy and strong and can withstand a little force from your fingers without losing their shape.

tubes and rods

knitting needles cut to handleable size for rolling and curving

• Knitting needles - all thicknesses will do. Avoid plastic ones, they are too bendable. I got mine in thrift stores. They may be used but they're cheap and will do the job. I have sawn some of them in more hand-sized pieces for easier usage when rolling cones and little cylinders.
• cylindrical plastic curtain rods, toilet and kitchen paper rolls, The flat sticky tape ones that you're left with after the rolling off all the tape, it all does a wonderful job. It's all about getting as many sizes as you can get.

Knifes
Just one good Xacto(ish) knife will do most of the job perfectly. Change blades every so often, nothing's worse than trying to cut with a blunt blade. Don't buy the cheapest knife and blade sets, though, they will break or have a bad fit and do you no good.  Mid-range are fine. As an extra you could look for a double-blade holder to be able to cut perfect small strips of paper. There also are small knifes (by Olfa) that can rotate when you cut out complex shapes but I have never tried them and I have never needed them up til now. But they might be handy.

double-barrelled knife!

For small corrective cutting I sometimes also use tweezerscissors. It requires a steady hand. Mostly I can do all the stuff with just the knife.

Also, do yourself the favour and buy a good cutting mat. Don't be cheap and take a nice large one. I use an A2-sized mat, which in my eyes really is a perfect size.

Detailing
For riveting I have made something out of a powertool-sized circular sawblade I can run over my paper to imitate nicely spaced riveted lines. Be creative and make one yourself. There are small sewing tools for sale that look like this  but they have a large interval between the indents. For an average scale size it's better to use aforementioned sawblades. They're fairly cheap. You can also take apart an old wind-up alarm clock for cogs and sprockets.

Holes and circles
Nothing comes close to my hollow punches when it comes to make perfectly shaped round holes in paper. You could try and use other tools but these are the best. Take my word for it. Collect them from 2mm to 20 mm at least. 

The smallest ones might be a little painful in the flesh of your hand while pushing. I "invented" a little way around that by adding the corked bottle cap of a sherry bottle (or whisky or port or whichever drink you prefer). make a hole in the cork and push the hollow punch in. The small ones are the ones I use the most, so they might as well be comfortable in their use.

For holes beyond that, there's this guy:

largest diameter

smallest diameter - this is kind of tricky in use, I have to admit.

a circle cutter. A compass cutter really is much less convenient. They're a bit expensive but worth every cent. The central stem ends in a flat round rubber base that leaves no hole in the cut-out circle. You can, however, unscrew that and have a sharp pin to get more grip. The fastening screw goes over a plastic shaft. Careful with this, too much torque can tear off the plastic shaft. Other than that, it's worth all 30 euros.

For rounding and smoothing curved shapes I use embossing tools. For glued pieces as well as single parts that need more smooth roundness they work fine.

For gluing, I use any generic white (wood) acrylic glue (PVA) and Aleene's clear gel tacky glue. For applying I almost always use cocktail sticks. They're cheap and you can be very precise with them.

Other stuff I use for shaping (but also for model details - I am not a purist in any way) are balls in all sizes and materials. I have collected a lot of them. Here too, the thrift shop is your biggest friend.

fake pearl beads, wooden beads, styrofoam ones, ping pong balls, even the roller balls of deodorant appliers are great.

Now I am not at all good at maths and calculus in general. But I figured out how to use scale charts and up- and downsizing methods. For this stuff I need rather precise measure tools so I got myself a digital calliper. It works both ways, I can measure stuff I made and check the scale and I can work measurements and apply the data to my model parts.

Other stuff I have are of course clamps for keeping glued stuff together (I also use clothes pins for that purpose but I turned the parts around as you can see on the picture. It gives a more pinching and flat grip than the way it is originally made.

Maybe it is a bit luxurious, but I happen to have an A3 printer. This means I can print out and size stuff up very easily. In general, my models are quite small but it really has some advantages. This one even lets you run one single A3 sheet through a rear manual feed. Also, I always scan models I buy. That way, you can always redo it without having destroyed the original. Furthermore, you can enlarge of reduce the scale to your own preferences. But in the end, having the possibility to print at A3 is pretty nice indeed. And the price of an A3 printer isn't that far from that of an A4 one.

And well, the most important stuff of course is what we're working with: Paper. 
I'd suggest you collect a fair amount of paper. Any size or colour. It will always come in handy when you have to reinforce something invisibly (then it doesn't matter which colour it is). I also have a collection of metallic paper and textured paper. I also often use photo paper (both gloss and satin) to get a more realistic effect on rocket or aircraft fuselages. It doesn't have to be expensive, I sometimes find a big collection of paper at -again- the thrift store. Some tips: For regular paper, I almost always use 200 g/cm2 but 180 or even 160 is good too. Photo paper is tricky, lots of it is not even really good for model making at all. Sometimes the gloss layer can't stay on an peels off. I prefer thick professional photo paper. And I prefer satin gloss, because I often think high gloss is too much for scale models. The ivory shine my solid rocket boosters have makes them look so realistic. Something I doubt would look good with high gloss. But that again is working well for say, 1/35 car models or perhaps even commercial airliners.

Small card. Just hobby paper from cheap stores. The thin stuff can also be used to roll cylinders from thicker paper in, around a knitting needle, for example. This way you protect the paper of the model kit by rolling it into 'expendable' paper and put it aside to get used to its new rolled-up shape. The lowest tray has sheets of photo paper in it. I often buy stuff at the thrift shop (10x15cm photo paper for example) but I also bought very expansive Satin gloss A3 paper at the art shop. I recently discovered the awesome crisp sharpness of matte photo paper. Incredibly deep colours and super sharp results. For regular hobby stuff however, I think most photo paper might be a little too much... (-:

Really thick coloured paper. 250 grams or even thicker. 300, 350. Good for backing up but also for making sturdy little coloured models. Just make sure you spray it with UV- spray. Otherwise it will soon discolour badly. You can, if you have a pile of paper in an odd measurement or size like this pile of German coloured hobby paper books at the photo up above here, introduce it into your printer's memory as a special custom size.

And lastly, make sure you keep a backup of all your precious paper model files. You never know when (not if -- WHEN) your harddisk is going to die on you.

This was my tool story, hopefully I have given you some tips. 
--PK