Currently the only well-supported host-based hardware RAID controller (i.e, a controller for which there exists a driver under Linux) is one that is made by DPT. However, there exist other host-based and scsi-to-scsi controller which may work under Linux. These include the ones made by Syred, ICP-Vortex, and BusLogic. In addition, there exist plenty of SCSI-to-SCSI controllers. See the RAID solutions for Linux page for more info.
If, in the future, there is support for other drivers, I will do my best to incorporate that information into this HOWTO.