I've had a set of JBL Creatures hooked up to my G5 Dualie since I got it in 2003; they're passable when needed, but I rarely use them. Most of my casual listening & work in Logic Express involves a good set of headphones.
Whenever I get my next machine, whether a 27" iMac or perhaps a Mac Pro, I'll continue using headphones most of the time, but I will add some basic monitor speakers for occasional use, likely something like
these.