Amazon has the PNY OPTIMA 4GB memory kit for just $29.98 shipped after rebate, originally priced at $61.99. It’s “compatible with PC2-5300 (667 MHz), PC2-4200 (533 MHz), and PC2-3200 (400 MHz) systems.” Product page.

4GB Kit (2x2GB) PC2-5300 667MHz DDR2 Desktop DIMMs. Easy to install / Low-latency modules / DDR2 / 667 MHz / Contains 2x 2GB Pack.

[via Amazon]