Given allot of games are ports nowadays your more likely to have problem with getting 16:10 support then 16:9, that said its extremely rare to have a modern game not list ether 16:10 for 16:9 resolutions. The only real difference will be if they properly correct their FoV for the different aspect ratios, that information you'll find all over this site so you'll need to look it up on a game by game bases there is no single answer for all games.
Thanks Skid. I expected current games to support both, but my backlog of games waiting to be played includes games from every year from 1997 to 2010 (except 2008, guess I played everything I wanted to play that year), so I'm glad I had a buddy who mentioned this place to me a while back - I'm very impressed by the breadth and depth of the database of older games represented here! It looks like for the most part after a cursory glance most of the hack/ini/command-line/etc. methods allow for "custom" resolutions (by which I mean, enter your own rather than choose from a list), which solves the main thing I was worried about (having to choose an aspect ratio that doesn't match my monitor).
Game on!