The standard today is 1024x768
1024 on 768 on most budget 15" monitors is a nothing but a big headache-inducing flicker -- don't underestimate the number of people who still run 800x600 or lower.
According to the following, about a 3rd of people online still use 800x600 by default:
http://www.onestat.com/html/aboutus_pressbox22.html
(June 2003)
The most popular screen resolutions on the web in the world are:
1. 1024 x 768 48.3%
2. 800 x 600 31.7%
3. 1280 x 1024 13.6%
4. 1152 x 864 4%
5. 640 x 480 1%
6. 1600 x 1200 1%
7. 1152 x 870 0.2%
Personally I would choose 800x600 over 1024x768 for a full screen game any day, or even 640x480 for graphic-intensive 3D games. I run windows in 960x720, which is the most pleasant one to look at for any length of time on my 17" screen.