Newegg has a 2 x 2GB kit of OCZ DDR2-800 desktop memory for $79.99. There's a $30 mail-in rebate to bring the price down to $49.99. Shipping is free.

Rebate good from 8/17 to 8/31, and must be postmarked within 12 days after purchase. This is a different kit than the one at ZZF for $50 shipped AR. Stock timings/voltage/speed are the same, but it's a different model.

Capacity: 4GB (2 x 2GB)
Speed: DDR2 800 (PC2 6400)
Timing: 5-4-4-15
Voltage: 2.1V