One of the best SSDs from a dollar per gigabyte perspective is the Samsung 840 series; you can see it in action here in Allyn's review of the 250GB model.  It uses Triple Level Cell flash, which is what helps keep the cost down, but won't have an effect on the performance for most users. 

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Samsung 840 Series 120GB SATA 6Gb/s 7mm 2.5" SSD (MZ-7TD120BW) @ $100