A little collection, copied from
http://www.crafty-games.com/dnn/DesktopDefault.aspx?tabid=71&pageID=355&pageName=
The links aren't copied over, but could google for most of them.
Modern
Hasslefree 28mm UK Hasslefree reviews (1 Review) - Kev White's miniatures company - the 'Adventurers' range is the one you want for modern figures, with a variety of 'zombie hunters' as well as a few figures clearly inspired by films.
SJ Games 28mm US SJ reviews Mostly out of print, though according that site Steampunk Miniatures are still available. They also do some Cardboard Heroes - sheets of heroes that can be punched out and folded up and used as miniatures.
Ground Zero Games 25mm UK GZG reviews - Looks to be quite a selection - though be warned most don't have pictures. The Street Level range seems to be where most generic modern figures lie, though the 'Characters' section has some and if you dare to look there are some Bond-Girl-esque types in the 'Gentlemans Collectables' section - though you have to scroll through some gratuitous pewter nudity to reach them.
Tactical Miniatures 28mm US Tactical reviews - Small selection consisting of various types of police, terrorists and hostages. The hostages tempt me as they are the one type of civilian that you want to know where they are in the room and I've not seen anyone else do them.
Superfigs 28-30mm US Superfigs reviews - Mostly superheroes, but some civilians packs in and amongst.
Copplestone 28mm UK Copplestone reviews - The 'Future Wars' section is what you want - has a good selection of cops, men in black, bikers and the like.
Wargames Foundry 28mm UK Foundry Reviews (1 Review) - The Foundry's Street Violence line is a an excellent collection of all sorts of modern heroes and antagonists, including soldiers, cops, gangsters, rioters, killer street walkers, bikini babes, angry midgets, and more!
Military
Black Scorpion 32mm UK Black Scorpion reviews Adam Clarke's miniatures company - Does some Iraqi Militia & U.S. Marines, a couple of the Desolation Row figures are more 'adventurer' style modern figures too.
Steve Johansen Miniatures (can't find a scale) US Steve Johansen reviews - Seems to be mostly military on the site with U.S., Terrorists, Russians & South African forces.
Copplestone 28mm UK Copplestone reviews - The 'Future Wars' section is what you want - the troopers are generic, though look US inspired to me.