Seagate, Maxtor, Hitachi and Fujitsu all make a 15,000 RPM SCSI drive. The fastest SATA drive is the WD Raptor right now.
SCSI drives are expensive, for several reasons. The biggest factor is the fact that the people who buy SCSI typically have extremely high MTTF requirements. (Mean Time To Failure)
Your typical desktop drive head media interface is designed right at the knee of the curve, so to speak, on the head media performance... Desktop drives (Cheap drives) don't have a lot of margin... So they fail at a much higher rate... They have all sorts of head degradation problems, etc, etc... The people who pay $800 for a 146 GB drive absolutely will not accept that kind of problem... And they shouldn't!
The 10,000 and 15,000 RPM drives all have another factor working against them, and that is they all use smaller diameter disks than the lower RPM drives, to reduce the imbalance problems that arise from spinning up so fast... You can see that in the picture that Hitachi has on their web page for one of their 15,000 RPM drives.
http://www.hitachigst.com/portal/site/en/menuitem.191a33649dd96d1d92b86b31bac4f0a0/
Fujitsu's drive page also has a good picture
http://www.fcpa.com/download/download/hard-drives/mau-datasheet.pdf
The smaller disks translate into much smaller capacity... The outside zones of a 3.5" hard drive have a lot more sectors, and therefore a lot more storage... The OD disk area is golden to hard drive designers...
SCSI drives are generally very reliable... I have always used SCSI drives in my computers, and as I upgrade some of the older drives get recycled into other PC's... My youngest son's computer has an 18GB Seagate Barracuda that has to be 12 years old in it, and it still works flawlessly... It's a dinosaur; it's the old 1.62 inch high drive... I just looked at it a couple weeks ago, and it has no grown errors... The only errors are the ones it had when it was brand new... It's been in use daily that whole time except for maybe a month or so... I still have a 2 GB Quantum Atlas that I use to back up documents that's even older than the Barracuda!
For high performance at a reasonable price, The Raptor is the best deal out right now. Since they incorporated command queing in the SATA drives the performance is right up there with SCSI... You pay a premium for the 10,000 RPM drive, but it's still a lot cheaper than switching to SCSI.