Vertex 3 120GB is horribly unstable. The firmware is busted and you'll be lucky to keep it running for more than an hour at a time.
Vertex 3 240GB is apparently fine, but it costs a ton.
IMO you're best off going with a single Crucial C300/C400. Since pretty much all the new Sandforce SF-2281 drives are having issues, and SF-15xx drives had their speeds knocked back by denser NAND, you really are best off with a C300/C400 or Intel SSD.
C300/C400 are faster, so I'd go for one of them. Apparently Intel and Micron have a joint venture, so Intel's SSDs and the C300/C400 are using the same NAND? (should be similar reliability)
Check the Online Deals section
for good deals on SSDs.
C300's are coming on sale a lot recently: