If you already have the Samsung monitor, I'd suggest getting a matching one. I've tried two monitors in the past and I found it best for my eyes and lack of headaches to have them matching. To put it a different way, I started out with a 22" CRT and a 22" lcd and it drove my eyes buggy looking from one to the other. I changed to two LCDs and the headaches and eyestrain went away.
I myself have been thinking of getting a 24" widesreen, but it requires a lot of video card power when gaming, like using SLI or Crossfire for the best frame rates, detail, etc. So far, I'm sticking with the Samsung 22" 226BW. If you haven't bought the Samsung monitor yet, then a single 24" monitor may be the best way to go. Just my opinion.
This one should be good. It has 16.7 million colors (it's a better panel than those with 16.2 million), a decent response time, it's non-widescreen. Maybe also look at LG and ViewSonic for other good options.