I've got a dual 1.8 G5 w/ CS2 suite + umpteen other programs pushing two 21" LCDs. I have roughly 1.5TB of drive space across multiple external drives +2 internal. As a file server, I have an old dual 450 G4 sawtooth doing the dirty work of automated tasks for things like keeping various web pages updated for client work and file backups, and a black MacBook for getting stuff done while sitting on the couch. Add to that an iPod touch to let me access mail + web things while out of the office at client places and random coffee houses, and I'm pretty complete.
For output (which you'll need some form of, by the way) I have a now-aging HP 2550ln networked color laser for regular sized proofs, and a crappy little HP 1220Cxi multifunction printer/copier/scanner that does all my scanning, which isn't much anymore, hence the crappy scanner. Anything that requires better equipment that I have to work with at my fingertips I use a friendly local print shop to do for me - larger proofs, nicer scans, short print runs, etc.
The G5 tower will be replaced this summer with whatever the middle-ground Mac Pro of choice is, unless I can finally convince myself to go to a true mobile format and move all my day-to-day work stuff over to a MacBook Pro. Haven't made my mind up with that - the stopping point had been not being able to use both big monitors, but I see there are various external display cards on the market now for doing that very thing. I doubt I'll sell the G5 though, instead I'll probably convert it into something my kids would like to use and put it upstairs for them with the parental controls set pretty heavy on it so they're relatively limited in their use of it.
I'd post a pic, but I'm lazy and tired - imagine a tower with 2 decently large monitors on a standard wooden desk w/ wireless stuff talking to it. Visualize whirrled peas.