I've found OpenOffice to be very slow compared to the actual Microsoft Office for Mac. If you have some budget, I'd recommend that over OpenOffice.
I can second the recommendation for QuickSilver - it's one of the best launchers I've used.
For IM clients, if you have contacts outside of the AIM network then you may want to try Adium - a free multi-IM-network chat client that has handy things like searchable transcripts.
Another general utility that I highly recommend is iStat menus - it gives you a realtime monitor of CPU, memory, disk, etc. right in your menu bar.
