There are only 2 30" 2560x1600 monitors on the market (that I know of) - the Dell 3007 and the Apple 30" ACD.
Both require dual-link DVI output to run properly, currently this means that the following can work with the 30" LCD monitors:
- Mac Pro
- MacBook Pro
- Certain recent version of the PowerBook
- Most, but not all, PowerMac G5s.
There are larger displays out there but most of them are just that - displays - they have a lower resolution (normally around either 1920x1080 if they are LCDs or 1366x768 if they are plasma screens) and are mainly designed to be used as televisions or to display information at a size that is visible from a long way away.
How much does the Dell 3007 cost anyway?