These Infineon 1GB dual kits are on the Asus QVL, and Komusa tech support said they'll work with the P4P800-E Deluxe
http://komusa.com/1gbkit5pc40d3.html
1GB kit (512MBX2) PC-3200 400MHz Dual Channel DDR Infineon Technology /
Micron
$159 for CAS 3, $5 more for CAS 2.5
The Samsung are also on the QVL, and Komusa guarantees they're compatible:
http://komusa.com/sa1gbkit5pc4.html
1GB kit (512MBX2) PC-3200 400MHz Dual Channel DDR SAMSUNG
$160 for CAS 3
The Corsair or Mushkin 2-2-2 ram costs around $300 and up.
I'm tempted to get the Infineon.