OS X on a MacBook Pro. Best *NIX experience I've ever had on laptop hardware.

There might be small bumps in a SYSV-vs-BSD sense between Solaris that you're used to and OS X, but probably most any open source utilities that you want will compile out of the box (either by hand or via something like macports). Leopard comes with 5.8.8 stock (or you can roll your own 5.10 from source).

Update: Fink is certainly another viable option; I used to use it but switched to macports