It's unlikely new Mac Pros are coming before Christmas. It's far more like new Mac Pros are coming sometime in January.
If you're looking at an iMac, a Mac Pro is likely more than you need, so it should last longer than if you buy an iMac. If you're on a budget, I wouldn't buy the display from Apple, there are other less expensive monitors that are just as good as Apple's.
-- Mac Pro Dual 3.0 Dual Core, 4GB RAM, 150GB Raptor HD, 500GB HD, Superdrive, Radeon X1900XT, Bluetooth, Airport Exteme, Logitech Z-5500 5.1 Speakers, 30" ACD
-- PowerMac G5 Dual 2.5, 2.5GB RAM, 160GB HD, Superdrive, Radeon X800XT, Bluetooth, Airport Extreme
-- Macbook Pro 2.53 15", 4GB, 320GB HD, SuperDrive, Bluetooth, Airport Extreme