Adapting game resolution to screen
Solution 1:
I've always set this option with my video card settings... I know for sure nvidia does this. Not 100% sure ATI does, but I find it hard to believe they don't. May need to update your video card drivers, but it's well worth it to me.
Solution 2:
The Widescreen Gaming Wiki and Forums have solutions for many games. For individual games that are not covered there you can always ask us, however :)
For Deus Ex, Google suggests this tool. The problem is that apparently Deus Ex reads screen resolution from a .ini file, then overwrites the custom field with default ones at every launch (source with batch file workaround).