I've bought the syba card and I'm happy with it. $20.45 got me the RAID version shipped.
If the longer warranty makes you happy, go for the SIIG. IMO it's a waste of money.
If you look carefully, you'll notice that all these cards use the reference siimage drivers, so the price difference is only in the branding and possibly pcb.
According to the siimage site, *ANY* card with flash chip is cappable of RAID; there is only one version of the SIL0680 chip and it is RAID capable. The syba card comes with an AMD flash chip.
Also note that (all?) these cards are 5volt PCI 2.2, so you won't be able to use them in a PCI 3.0 / PCI-X system.