Muscle Gauge kind of blows the competition out of the water when it comes to the selection of flavors it offers (cake batter, anyone?). The problem is that it's become wildly popular, so you're kind of out of luck if you don't buy quickly after one of the few online sites that carries it restocks inventory.
for future use, though, and just check intermittently. That's where I always get mine; ridiculous fast delivery, cheap flat-rate shipping and they'll usually throw in some awful free magazine with workout babes on the cover.
Since it looks like everything that isn't a fucking 25-pound tub of vanilla is sold out at the moment, check out True Protein. I haven't used the, but have heard good things. Custom mixes/flavors available and prices look good for what whey costs elsewhere.
There aren't a ton of affordable whey isolate options out there, though. Plenty of concentrates to pluck from, but hell with those.