Standard CRT monitors display images with a width-to-height ratio of 4:3. Widescreen resolution has a typical ratio of 16:9 or 16:10.
852x480, 1280x720, 1280x768, 1365x768, 1920x1200 are common widescreen resolutions used.
As far as UI's go, most authors follow two basic patterns. Customized graphical bars that work with only certain resolutions (
AYA UI) or customized windows that work lilke lego's for you to layout on the screen (
X60). You just got to find one that works for you in the "lego" sense to fit in nicely with the widescreen.