OCZ's ModStream 450 is fairly popular as is Antec's NeoPower 480. The Sunbeam NUUO550 is the only nVidia SLI-certified modular power supply on the market right now. Newegg lists that sucker for $79.00, which given modular factor and Sunbeam being relatively unknown in the power supply business, it's price is damn near amazing as I'm pretty sure it's cheaper than the OCZ and Antec unit's I mentioned.
I haven't used Hiper, but I've been hearing some good things about them. The UK lads that hit this place up tend to favor them or Tagan units.