I purchased the bulk of necessary construction tools from Cleaveland Aircraft Tool. I opted for their complete airframe tool package. So far it seems to have everything necessary to get started and not too much of anything you don't need. I've been happy with everything I've used so far. Based on recommendations from others, I bought the kit with a Taylor 2x rivet gun and also purchased a Taylor 3x gun from Professional Air Riveting Tools.  Opinions run the gamut as to whether 2 guns of different size are needed. I'll soon find out, as I am just about ready to start some riveting.

The section in Van's manual regarding the necessary tools covers most,  if not all of what's needed and obviously they know what they are talking about.

Here are some must haves:

Air Compressor - (duh) DO NOT go with an oil-less type unless your already hard of hearing. I got a nice oil lubed 7.5 hp 60 gallon Porter-Cable from Lowes' for less that $350 (clearance -  and it was a 220v unit but hey, I've got the "Wall of Power".)

Drill Press - I got a nice 9" Craftsman Benchtop model for less than $100. A must for machine countersinking.

Bench Grinder - Handy for putting final touches on fabricated parts. Also used with scotchbrite wheel for cleaning up edges of material, although I still have not found the touch on this because it seems the scotchbrite wheel is too coarse and leaves edges kind of rough.

Clamps, clamps, clamps - Assorted shapes and sizes, can't have too many.

Nice to haves:

Pneumatic hand squeezer - I have not gotten to the point of needing one yet (haven't even got to any riveting) but if you can afford to plunk down $400+, more power to ya. I think I'll find one to borrow.

Parts drawer organizer (or 2) - Ideal for all the small parts you get in the bags with your kit. Also handy for drill bits, deburring bits, and other small machine parts.

A computer close to or in the shop - There is a wealth of information and many builders web sites on the internet. It's like having a partner in the shop with you. I am also using Kitlog Pro for my log book. (Remember to back up regularly).

Depending on your neighborhood, consider a security system for your shop. You will have quite an investment in tools and material. I read of one builder whose shop got broken into twice in three days. I already had a system for the house and just added a couple more points to the garage. I also had them install a heat detector due to some of the hazardous/flammable materials that the project requires. This is definitely worth the peace of mind.