I was surprised at how many tools I ended up using while I was building my plane. Forunately, I had most of them so I didn't have to make a huge investment in new tools. Of course, if you like tools, getting new ones is never a bad thing.

DISCLAIMER: I don't make any claims that any of my advice is good and/or accurate. This information is knowledge that I've picked up along the way and has worked for me and/or for other people. If you ruin your plane because of something that appears in these pages, I take no responsibility for it.

DISCLAIMER: The web sites that I refer to are there simply for reference and are in no way, shape, or form an endorsement for the site and/or the company that owns and/or manages the site. I provide these links so that you can see what I'm talking about and get an idea of what to purchase.

Patience First and foremost, you have to have patience in this hobby. If you are not a patient person and/or are not interested in becoming a patient person, then I strongly urge you to turn back now and never come hither again! This hobby takes time and practice. It's a lot of fun, but only when you can be patient with yourself and the learning process.
Screwdrivers What project would be without screwdrivers? The problem is the number of screwdrivers that you may need! At a minimum, get yourself one of those Workforce driver sets. It's like a rachet set, only with interchangeable drivers instead of sockets. Some of the screws are quite small in airplane kits so be sure you also have a precision screwdriver set.
Rachet Set Most of the screws, nuts, and bolts in a plane kit are small so when you're looking for a set of rachets, make sure it contains small sockets. In addition, some kits are metric while others are SAE standard sizes. If you're looking for a full set check out the Craftsman 190 pc. Mechanics Tool Set with Easy-To-Read Sockets at Sears. You can't go wrong with Craftsman tools and this particular set should have everything you need to build a plane as well as repair a car! This set contains both metric and SAE standard sizes.
Box Knife/Utility Knife You'll need to open your kit with something and a box knife or utility knife like this Husky Autoblade Utility Knife will do the trick. You'll also use this knife to do other general cutting as you build your plane. If you need to make precise cuts, don't a knife like this one. Use an Xacto knife instead (see below).
Hand Drill/Dremel Imagine working on a thin piece of balsa wood with a 19.2 volt high-speed drill! Okay, I can because I did. That's a little too much power for the application. If you like power tools and have the cash, pick up a Dremel tool (also called a Rotary Tool). If you don't have that kind of cash, pick up a hand drill. Most of the drilling you'll be doing will be precise. This X-ACTO 5087 Deluxe Hobby Tool Set is REALLY nice in that it contains a Pin Vise (which holds small drill bits) and other assorted tools, most of which you'll use at one time or another.
Precision Drill Bits The X-ACTO 5087 Deluxe Hobby Tool Set I mentioned above contains three drill bits (I'm not sure of the sizes). If you need additional sizes, check out either this Xacto - Drill Bit Set with Stand or this Xacto - Carbon Twist Drill Bit Assortment (Fine) set.
Precision Knife Set I already mentioned the X-ACTO 5087 Deluxe Hobby Tool Set above which contains various tools. If you're just looking for the knives without the other tools, here's the X-ACTO 5083 Standard Knife Set that would work.
Level Since your plane has to be built with some precision, having a level on hand is a good idea. You don't need a huge one. Something like the Klein Torpedo Level with Heavy-Duty Magnets would do just fine.
Precision Files Unless your kit is built perfectly, there is a good chance you'll be doing a little sanding and filing. This isn't a bad thing, it's just something to be aware of. You can get a set like the Xacto - Needle File Set which should contain everything you'll need for this task.
Pipe/Tube Bender A pipe bender is used to bend aluminum or brass piping. This type of piping is inserted into the fuel tank stopper and the gas line as well as the pressure/refill line is attached. Some kits may have pre-bent piping while others will not. I haven't found one of these online yet, but your local hobby shop should have them, or at least know what they are and where you can buy them.
Metric and Inches Ruler/Measuring Tape Since kits come in both metric and SAE standard sizes, having a rule and/or a measuring tape that has both scales is a good idea. Often the kit instructions will tell you that a certain part of the plane needs to be at least or exactly so many inches or millimeters from another part of the plane. You can find these are a hardware store or your local hobby store. One such ruler is this 36" ruler.
Hex Wrenches Hex bolts or socket bolts are common in plane kits. And again, they come in both SAE Standard and Metric sizes. A good set of wrenches like these Ball Point Hex L-Wrench Sets is good to have. You will probably want to have both size standards to allow you to switch between metric and SAE.
Triangle/Square The primary use for this tool is to make sure that the rudder and the rear wing are at a 90 degree angle to each other. You can get the Builder's Triangle Set which has a triangle with its corner cut out so that it can sit against the rudder without interfering with the fusalage.
Clamps You only have at most two hands and sometimes you need more. If you don't have an assistant, you can use various clamps to help out. C-Clamps, for example are useful when gluing two parts together. Rather than holding them together yourself, use a clamp. You can also use a clamp with the two pieces of thin wood I mentioned on the supplies page. There's no need to get heavy duty clamps as most of what you will be working with will be small and delicate.
Pliers, Scissors, Wire Cutters, Wire Strippers These tools always come in handy, and usually are necessary for completing a plane kit. Be sure to have a good pair of needle-nosed pliers and some sharp scissors. The thing to keep in mind here is that you will be working with small pieces so there is no need to get heavy-duty tools. The only heavy-duty tool I can see using is a set of lineman pliers. I use these to cut pushrods when they're too long.
Miscellaneous Tools Other tools that you will probably need include sharpened pencils, shop towels (particularly for the glue!) masking and/or electrical tape, various fine grades of sand paper (150 to 400), and small or micro brushes for glue.