Which make drives is down to you - they are all pretty reliable and mostly the same speed, until you start getting into the velociraptor type area, but then you'll easily notice it in the price difference!
500GB is normally about 40-45 per drive, 1 TB is 65-70 per drive.
I think your motherboard supports RAID 0,1,5 and 0+1 out of the box. You can find more info on them on wikipedia but here is a summary.
Raid 0: "joins" the drives into one big drive. You keep full capacity of the drives (i.e. 2 1TB drives = 2 TB), read access is technically doubled, write access up to doubled as well. However, this has no reliability - if ONE drive fails you lose ALL the data. You can RAID 0 any number of drives together, 2 or more.
Raid 1: "mirrors" the drives. You get capacity of one drive (i.e. 2 1TB drives = 1 TB). Read access is doubled, write access is about the same as 1 drive. This has reliability though, you can lose all but one drive and not lose any data. You can RAID 1 any number of drives together, 2 or more (but remember that doesn't give you greater capacity, just more reliability and read access)
Raid 5: complicated to explain, but is somewhere between 0 and 1. Takes a minimum of 3 drives. You have the capacity of all drives minus 1. (ie, 3 1TB drives = 2TB, 4 1TB drives = 3TB). Read and write access about the same as raid 0. However, it can tolerate losing ONE drive and one drive only.
Raid 0+1: Raid 0 and 1 together. Takes 4 drives minimum, can support up to 2 drives failing. Gives massive read speed and good write speed. You get the capacity of 2 drives (i.e. 4 1TB drives = 2 TB capacity). Best all round performance and reliability, but takes a lot of drives.
What you go for depends on your backup strategy (if any) and how much money you have burning a hole in your pocket. Consider also having a small capacity SSD (128G, say) for your OS and programs, and 1 TB or more behind it on regular drives for data files.
Good luck!
