I have just bought a LSI MegaRAID SCSI 320-2X for a PE 6600, it runs in one of the 64-Bit 133Mhz PCI-x slots on the motherboard, You can upgrade the RAM onboard upto 512 if you need to from the standard 64Mb.
I have upgraded from the Perc 3DC due to performance issues and found lots of forum posts about how good the LSI Megaraids are.
Look on the Scan.co.uk website for cheap prices.