With my PowerPC Mac (running OS X 10.3.9), I have been very happy using VNCViewer, which can be downloaded here:
http://homepage.mac.com/kedoin/VNC/VNCViewer/
However, the performance on OS X Tiger (10.4.x) is poor, and it's even worse if you have an Intel based Mac. The only VNC Client that is currently up-to-date enough to be a universal binary is Chicken of The VNC, which can be found here:
http://sourceforge.net/projects/cotvnc/
The latest version is still beta (2.0b4), but it works rather well. There is one very annoying bug to be aware of, though. After switching to full screen mode, the software acts like the Ctrl key is being held down, so all your mouse/keyboard actions either don't work or have unexpected results. The workaround is very simple, once you know it -- just press Shift and it clears the Ctrl key lock. The bug has been logged already, so hopefully it will be fixed in the final version.
Just thought I'd add another name to the pot: RealVNC.
http://www.realvnc.com/products/beta/macosx/
I've just been Googling for a Mac VNC client for my new Intel Mac, having used VNCviewer for a good while on my previous G5 Mac.
I tried the latest Chicken of the VNC, which worked, but it was rather sluggish. I also discovered RealVNC, and the difference is amazing. I'll be sticking with RealVNC for now, thank you.
YMMV of course, but for using my MacBook Pro to control the Ubuntu Linux box downstairs, RealVNC gets my vote.
Thanks for the suggestion Tim! I have used RealVNC on Windows, I didn't realize they had an OS X client available. I will give it a try.
Thank you.. thank you... for posting the link for VncViewer for Mac OS X. I had almost given up looking for a vncviewer since chicken VNc does not work well on iMac OS X - gets "rectangle encoding error".