Which One?

Sometime in the future (hopefully near) I plan on replacing my G3 600Mhz iMac with something a little more up to date. My biggest problem during this planning is whether to buy a desktop or a laptop. I really enjoy the power and the ability to add on to a desktop, and I have an enormous but nice Sony monitor. I also enjoy the portability and lack of cords with a laptop. Maybe someday if I have a job that pays really well I can have one of each, but for now I am stuck with power vs portability racing through my mind...