GPU has yet to be decided, but it's leaning towards a toss up between the Radeon 4890 and GTX 275.
What I'm looking for is a case and power supply that are ready for SLI and subsequent water cooling at a later date, but compatible with these parts for the time being. What's an appropriate case for this build and what kind of power supply is advisable? The size doesn't really matter, and I'm looking for practicality/price first, appearance second.
Case requirements for a water cooled system can get interesting. Have you read Conumdrum's water cooling guide over in the cooler and heatinsinks section of this forum? It is required reading. Here's the link:
The general rule of thumb is a high quality 750 watt power supply with sufficient current (amps) on the +12 volt rail(s) can power an overclocked system with two video cards operating in dual mode.
A high quality 750 watt power supply will have a +12 volt rail rated at 60 amps.
The Corsair 750 watt power supply mentioned by sirheck would be an appropriate choice. Corsair has a reputation for high quality power supplies that consistently earn high marks in technical reviews. They are stable, reliable, and come with a 5 year warranty.
Seasonic also has a reputation for high quality power supplies and they are often recommended by the veterans at this forum. Seasonics is an actual manufacturer that makes power supplies which are sold under a variety of brand names including the older Corsair power supplies. They also make power supplies under their own brand name. Seasonics released a brand new 750-X Gold modular psu that earned a coveted Gold Certification for energy efficienciency. The platform architecture is a brand new design that is not only energy efficient but also quiet.
Sunbeam actually started out making cold cathode flourescent light kits and wound up branching out into power supplies, cpu heatsinks, pc cases, and other components. Overall their own house brand power supplies are adequate. They do what they are designed for. They're just not stellar performers.
BTW - You should not skimp on a power supply, especially if you are going to be doing serious overclocking with a water cooled system.
First I'd ask if you really want to go to water cooling considering that peeps are having great success overclocking CPU's on air as much as 65% over rated speed.
To my mind, the case / PSU combo that stands out is the Antec 1200 w/ the CP-850 PSU. The case is great at air cooling, has a water cooling platform for reservoir or pump and the PSU is one of only three PSU's that I have seen garner a 10 in performance over at jonnyguru.com, it's also among the quietest and half the price of other PSU's in it's class. Look at Editor's Choice List and Recommended List here fr comparison purposes: