Here's a bit of an improvement on Panther screen locking. A previous hint suggested using the Fast User Switching (FUS) menuling to bring up the login window. This is a good method, arguably better than using the screensaver in many respects. But there are some people who don't want a giant chunk of menu bar real estate taken up by our names.
So, given that the FUS menu is just a regular menuling (for the most part), you can just drag it out of the menu bar, and it'll go away. Just be sure to do this while you're not in the Accounts preference pane, or it keeps coming back. After getting rid of the menu, download FUSKey and set a global key combination for bringing up the login window. Be aware that not all key combinations will work properly. Stuff involving Command-Option will likely not work, since that's tied to the Force Quit menu and the system won't respond to it. I've gotten it to work consistently using Command - Control - Delete, by which I mean the long Delete key, not the Forward Delete used in Windows' three-fingered salute. I haven't experienced any problems with my machine as a result of using FUSKey yet. This would seem to be a pretty solid screen-locking method.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20031105235442376