The thing with data cards be they SD or Compact Flash is to buy as fast a type as you can afford.
Cheap cards are best avoided,as they may be of suspect quality,or even fakes.
Sandisk,Kingston,Lexar,PNY,Sony etc are all reliable brands.
Basically the more storage space the card has,and the faster it is,the more expensive it is.
Shooting in RAW will use up much more storage space than JPG,so I would suggest a card minimum of 4 to 8gb at 30MB/s or faster.