MadShrimps has a very interesting take on a budget SLI setup for those of you who just like the idea of doing it. They built a "budget" SLI rig running two Asus N6600GT Extremes based on the NV43 GPU which fully supports their 256MB GDDR3 memory compliment. Here's an excerpt:

A few words on SLI. I cannot deny nVidia's SLI, while exciting at first is now thought of as a marketing gimmick which seduces the Gamer or PC-Enthusiast into spending twice the amount of money for two cards which produce twice the heat, require twice the power and take up twice the real-estate. The choice to release QUAD SLI updates in the future seems 4x as silly. The founders of 3DfX are more than likely rolling over in the proverbial 3Dfx grave, excavated while trying to integrate multi-GPU technology onto a single PCB. SLI reborn as Scalable Link Architecture IMHO probably coined the internal marketing phrase Profiting off the passion. Sadly we see this occurring throughout the PC-Industry. While I do respect Asus without whom there may be no "Enthusiast" since they were the pioneers of OEM, they are in the end a for profit enterprise

Pros
+ Solid performance in SLI mode
+ Compact and power efficient
+ Ran quiet and cool
+ Solid software package including Smart Doctor, Hyperdrive and Game Face Live
+ Great alternative for those wanting to try SLI without investing in other upgrades (i.e. SLI-specific PSU)

Cons
- Slightly dated
- May be hard to find 256MB version
- Somewhat pricey given the alternatives