You can't go wrong with either Sandisk or Lexar. Both build reliable memory cards.
I don't have a D300s but, I have been using Sandisk 8GB Extreme Ducati (45MB/sec.) and Extreme IV (45MB/sec.) cards in my D300 since it was introduced without issues. I have also used the current Sandisk Extreme(60MB/sec.) 32GB CF cards in the D300 without issues.