Microsoft's Remote Desktop Client for the Mac, which is PPC-only (not a universal binary), occasionally fails to launch on an Intel machine. The dock icon bounces forever, and CPU usage is high. To get it launching again, delete the folder ~/Library/Preferences/Microsoft/RDC Client -- apparently its preferences or default settings get corrupted over time.

I use rdesktop (compiled myself) under Apple's X11 more often, as it's much faster, and more configurable. For example, I have the display resolution with rdesktop set to 1600x1100 (command-line options in use: rdesktop -g 1600x1100 -z -xm -a16), so that it's max size on my 1600x1200 display, but does not overlay my dock.

Some kind soul packaged TSClient as in intel-mac .app. It's an X11 app, and probably rdesktop under the covers, but has a GUI.

** UPDATE: New/better link for TSClientX is http://desktopecho.com/tsclientx/
. And yes, it's redesktop and some other stuff (listed on that site) under the covers. It works!