Xbit labs has put up a very detailed review
on the MSI NX6800-TD128E video card, a lower-end SLI capable Geforce. It has fairly decent overclocking potential and is fairly easy on the wallet as well. SLI isn't something that has really taken off, largely due to price and lack of good support. That is changing, of course, and this hefty 24 page review goes into the pros and cons of low-end SLI configs. If you are interested in trying out SLI, read this through. Some of the improvements are fairly impressive.