Question : What is a good PCI-express RAID controller card

We have a Dell PowerEdge 2970 and want to add an external array of disks for storage. There will be a SharePoint database (roughly 10GB in size) but the rest of the space will just be for file storage. We were thinking 2-4TB for total size.  

We were looking at a PCI-e SATA Controller card and using enterprise class Seagate drives.

Realability is a must as the SharePoint database must be available at all times. There is not alot of traffic on the site (business is only about 50 users) but it is a business critical application that must be up at all times.  

Would we be better off going with a SAS controller card and SAS drives? Are there any RAID card brands anyone would recommend?

Answer : What is a good PCI-express RAID controller card

LSI by far, as not only do HP, IBM, Sun, NetApp, Dell, Supermicro, SGI, and more slap their names on LSI controllers, but the LSI chipsets provide the back-end expanders and chipsets for the RAID vendors.   goto lsi.com, look at the controllers and select one that meets your budget.  I would go with a BBU as well, as this provides additional performance/availability benefits, especially in a degraded mode.   Also look at the SAS-2 versions that give 6Gbit/second paths.  Go with the newer Seagate SAS-2 disks as well.  Also SAS has independent read and write channels, so you can get the disks to do a lot more work before saturating things, you also get a nice upgrade path and can support more drives.