I'd go for the G4 iMac. Think different! (he he)
I just got a 20" iMac 1.25 Ghz 1GB RAM and use it for photography with photoshop and it's alright. Not the fastest but it does the job. I mostly work with files around 6 MB. If you're scanning film or work with large RAW files, you'll want something faster. The screen is the same as the 20" cinema display. It is sharp and crisp (unlike the 17" iMac which takes it's screen from the 17" powerbook). Go see one at an Apple store. I was planning on getting a 20" display anyway, so the 20" iMac fit the bill perfectly.
I might be the odd ball here, but I really fell in love with the iMac's simple design and small foot print. I like being able to adjust the height, tilt and swing of the screen (sounding like a 4x5 photographer here). I've really been happy with mine.
Now I'm not saying don't get a G5. I'm just telling you my experiences with mine.
The main selling point of the iMac is of course the price. The memory discounts that Apple offers right now make it even more appealing because one of the two memory slots in the iMac is NOT user changable, so you must get Apple RAM in this slot. Apple is selling RAM right now for dirt cheap (by Apple prices anyway). Check it out at
http://www.apple.com
If you know a student or faculty that can buy this for you, you can get a 20" iMac 1.25 Ghz, 1GB RAM for $2200 shipped (from
http://www.apple.com). If you figure the monitor is the same as the 20" cinema display which cost ~$1200, the computer itself (with 1 GB RAM and superdrive) is only $1000.
So the way I saw it, 1.25 Ghz G4, 1 GB RAM, SD for $1000? Who cares about a 1.6 Ghz G5! $1000 is a bargain!