iMac
I have a TiBook and love it. HOWEVER, having seen the features in the top-end iMac, I am jealous. It is a better value. If I didn't need to bring my computer to work, I would really be kicking myself.
With the top-end iMac, you get a big screen, a processor fast enough to run about anything, a combo drive (!!!), and plenty of ports for connecting peripherals. Sure, you have almost no expandability, but it doesn't sound like you necessarily need it.
My 667 MHz G4 handles OS X just fine, but I wish I had the extra speed for the future.
I think the iMac is the best value out there right now.
Just my 2 cents.
CJM