I have pictures disabled for T-Nation at work so I'll throw out some posters names who have pic's and avatars up and hopefully they won't mind.
1) Skinny: Most of the beginner's at T-Nation. I'd consider anyone 6ft and under 180 skinny. Whether they're ripped or not, I'd still call them skinny.
2) My avatar and whatever pic I have in my hub of me over 200 lbs. I don't consider myself big, so I'd put myself here.
3)Big: H4M , BugeishAD (sp), NewDamage to name a few. I'd say if you're big if you're sporting 18 inch lean arms and are above the 220 mark at 6 ft.
4) Huge: Morepain, Syngergy, and Dave Tate come to mind.
5) Holy shit: Physiques of anyone competing at the Arnold or other high level shows.