Hi Stepes, yes you can add another SATA drive, I'm pretty sure your board supports RAID as well so that may be an option worth considering.
And which ones's better if there's any difference? Samsung, WD or Seagate?(same rpm's)
It's really a matter of personal preference at the end of the day, if you've had bad experiences with WD drives and nothing but good with Seagate ones, then Seagate would probably be the way to go. Just make sure you read lots of reviews on the particular drive you're interested in. I think those Samsung spinpoints are nice drives, also take a look at Seagates Barracuda range.
EDIT: madmonkey beat me to it lol
