Given all these options, if you're looking for a RAID solution, you need to think carefully about what you want. Depending on what you want to do, and which RAID level you wish to use, some cards may be better than others. SCSI-to-SCSI adapters may not be as good as host-based adapters, for example (see the DPT comparison between host-based and SCSI-to-SCSI adapters for why this is the case). Michael Neuffer ( neuffer@kralle.zdv.uni-mainz.de), the author of the EATA-DMA driver, has a nice discussion about this on his Linux High Performance SCSI and RAID page.
For the purposes of this HOWTO, I am assuming you have only a Linux system running. Also, note that I've only tried this out with the DPT Smartcache VI PM2144UW controller, with the DPT-supplied enclosure (SmartRAID tower), and I have no experience with other set ups. So things may be different for your setup.