I just ordered a new iMac with a huge 24" screen and it should be blazingly fast. The relevant specs:
2.8GHz Intel Core 2 Extreme
2GB memory
750GB (!) hard drive
8x double-layer SuperDrive
ATI Radeon HD 2600 PRO with 256MB memory
Plus it will have the new Leopard OS and iWork '08 pre-loaded, so I get both at no extra cost.