Since long time I'm using Transcend 8GB/16GB class6. Never any proplem. Cheap cards with lifetime guarantee.
Transcend class2/4/6 have ~ 18MBps read speed, class6 Transcends have 10-12 MBps write speed - more than enough for ALL cameras and ALL videos.
Transcend class10 ~ 14-16 MBps write speed - that's overkill .. but I bought it for testing (only few €'s more expensive, nearly same price like class6)
Worsest card I found: Kingston class6 with 6.5 MBps write speed :-(