I hate the way that the desktop background intrudes in the menu bar (due to its translucency), so I have edited every desktop picture I have (my monitor is set to 1920x1200) by adding a horizontal 21-pixel white bar at the very top, and a 1- or 2-pixel black bar just beneath the white bar.
Interestingly, Apple appears to have done the same thing on the main 10.5 installation screen, as its menu bar isn't translucent.
[robg adds: This is one solution to the translucent menu bar issue, but it's a fair bit of work. If you'd like to automate this solution, you might give OpaqueMenuBar a shot -- this piece of freeware (donations accepted) works by modifying the desktop images on the fly. It saves the modified versions to /tmp, and then uses that image for your desktop. While this solution works if you use only one desktop image, it didn't seem to work with my setup, which is set to auto-change the image at regular intervals. I've still got my fingers crossed that someone manages to root out some low-level opacity key we can modify to solve this problem for the menu bar as well as the menus themselves.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20071026065829864