What to look for in a new old HSF?

There's a used computer store in my town. They have a ton of stuff, including old heatsinks. I plan on modding a nice-ish one onto my MSI 6600GT (PCI-E) along with (hopefully) some smaller heatsinks (or I can make them smaller!) for my RAM.

What should I look for in a good device? I'll probably bring home several, given that they'll be dirt cheap.

Thanks all.

Probably look for physical damage on the HS itself, make sure it isnt twisted and that the contact surface is flat. Look far anything out of the ordinary, discoloration, rust, dings, cuts, scrapes, chips. I've heard old P4 HS make for really good mods. If they are dirt cheap, bring a few home and inspect them with a magnifying glass

I think if you are looking for second hand HS Arca_ex is right(how the hell can you warp thoses chunk of Al and/or Cu short of driving your car on the PC). Retail stuff I would look clearance, material, weight(unless you have thoses card support thing and for the love of god I couldn't name), base size(too big will be a pain to work and fit, too small and you loose cooling potential), fin density along with what fan you will need (think noise level also there).