Ok, so I've played Team Fortress 2 a bit and love it. The costumes are pretty simple, with some of the weapons and accessories being the difficult parts. I figured I'd start with the Engineer and do the others later.

The Engineer has 13 parts. (Give or take a couple)
1) Orange Safety Helmet (Worn backwards)
2) Welding Goggles
3) Work Shirt (Red or Blue) with a patch on each upper arm/shoulder.
4) White T-Shirt (Seen under the work shirt)
5) Work Glove (One only - Right Hand)
6) Dark Brown Work Bibs (Overalls/Coveralls)
7) Work Belt
8) Electrical Cable (Extension Cord. Appears to be missing the female plug.)
9) Small black pouch (Worn on right hip.)
10) Large Nail Pouch
11) Kneepads
12) Work Boots (Look more like military boots.)
13) Wrench (Pipe wrench?)

I've already got the Helmet, Goggles, Work Shirt, T-Shirt, and Boots.