Games that can't be run in widescreen resolutions will be stretched just because LCDs display them that way. Well some can display it 1:1, but then you got a little image in the center of your screen; not very immersive. So games like F.E.A.R are stretched like this for me because there are no WS resolutions. Thus I run something like 1024x768 filling my whole 1680x1050 screen so it doesn't look very good. This is the only game I have right now that can't be forced to WS but I don't care much because I'm not going to buy the game unless I ever upgrade my computer. Even a very-old game like NFS Porsche Unleashed has a widescreen toggle which just seems to put the game in a sort of Hollywood-like display.
Games like BF2 allow you to specify WS resolutions in the command-line, but as the above poster pointed out, actually putting this extra width to use requires the FOV to be adjusted with it. As he also pointed out, EA doesn't seem to include FOV adjustments in their games. A game like UT2k4 has 1680x1050 native but AFAIK you still want to adjust the FOV to take advantage of the extra width (i.e. being able to actually see more horizontally). So I run FOV 100 instead of default 90.
Then there's games like HL2 which not only support a load of WS resolutions natively, it actually adjusts your FOV to whatever your aspect ratio is. So 4:3 would see the least, 16:10 resolutions have a little higher FOV and see more, and the 16:9 resolutions have a slightly higher FOV yet to see a little more. Not sure what other games are like this, but it sure is cool.
Other recent games I have are Guild Wars and Savage. Both have a selection for 1680x1050 natively, but I don't know whether or not these dynamically adjust the FOV like HL2 (so you actually see more). I've taken comparison screenshots in HL2 but not with either of those.
My buddy has Quake 4 and told me it had widescreen natively, but I don't know if the FOV is adjusted. So you can have no widescreen (choice of stretching it or just displaying so that anything outside of that resolution is black border), widescreen that doesn't really do you any good but is proper aspect (like BF2), or kickass widescreen like HL2 which is very immersive to have the greater peripheral vision. Kudos to Valve, and lucky for me since I play DoD:S about 90% of my game time, but if you include all HL2-based games then its more like 97% of my game time.
