For those of us who are less Left-Coast savvy, could you give us a mileage estimate for the trip you're talking about? I spent some time in SD, but don't know how long your round trip is.
I've heard really good things about BMWs for long distance touring like that. Big fuel capacity, bulletproof motors, and hardbags to carry your gear. They're very comfortable. But the repair costs, should you need any, they're horrendous.
I hopped over on
www.epinions.com and didn't see any commentary on new Suzuki cruiser bikes. Looking on their site the Volusia doesn't look like it'll cut it, since it's smallish with no storage. The Intruder 1400 only has a 3.5 gallon fuel tank. The Marauder 1600 is AWESOME looking, 4.5 gallon tank, and I'm sure has accessories for luggage. But it's pricey.
There are a lot of good bikes out there, I'd say go drive some! Good luck.