I don't much like Fink or DarwinPorts very much. They have too few packages to be of much use to me. When I want open source apps, I launch X11 and ssh to my desktop with X-forwarding, then launch Linux/x86 apps remotely from my Mac. Since the two machines are on the same LAN, all Linux apps, GUI and command-line alike, run as responsively as if they were native. Set up some kind of file-share, like Samba, and you can effectively work in two environments from one computer, which works wonderfully for me -- twice as much processing power at my fingertips. It also means I can run some Windows apps on my Mac, via Wine/Cedega/CrossoverOffice on Linux/x86.
Before that I've tried Synergy2 and VNC but ssh with X-forwarding (with 2 screens) works the best for me so far.
If you've got the resources on your hands to try this, I seriously recommend trying it out (you may have to configure sshd for X-forwarding). If you only have a Mac to use, Fink and DarwinPorts are acceptable, although the software selection can be a bit sparse. All I use Fink for is irssi and screen.