I was always a big SCSI supporter, but I now feel the new IDE -100+ drives running 7500 - 10k RPM are just fine for hosting. If you can, I would recomend getting extra ram for the server to use as a cache (512MB).
It really depends on your the type of application and audience you're expecting. But EIDE *should* handle most applications effectively. However, SCSI is more scalable and uses dedicated channels for transfers.
Serial ATA do not offer that much of an improvement (last time I read an article it was about 1-2%).