I would say that the single most important piece of equipment for kit building is access to the RCU forums. The quality of craftsmanship and level of enjoyment you can achieve using this tool could only be surpassed by having a master builder at your side.

Another good tool is www.airfieldmodels.com

As for tools in the more traditional sense, as stated before, the list is long. I've acquired a large selection of tools. Number one most used is the #11 xacto knife, but there are many others that are indispensable, such as sand paper and sanding blocks, straight edges and rulers, clamps, a good buildboard, and adequate lighting. Then there are tools that are specialized such as covering irons, heat guns, and soldering irons. There are tools that you can build without, but once you have them, you wouldn't want to do without, such as a dremel tool and a good selection of bits, drill press, band saw, a precision miter saw and miter sander and so forth. Finding and acquiring tools useful in model building can become a hobby all to itself. I think that if I were to add up all I've spent on tools, I would even be surprised. My biggest tool purchase to date is a lathe/mill, at about $500 (not counting what I've spent on mill ends, lathe bits, clamping and other accessories). Not normally thought of as a tool, is the workshop you set up for building too.

Scott