Found this tip via LifeHacker. Here's what you have to do...

  1. Type Scrabble into Wolfram Alpha and choose Computation.
  2. Enter the letters you have in the Word box. Use spaces for blanks.
  3. A few seconds later, Wolfram Alpha will tell you all of the possible words along with their score (as shown below).

I imagine you could cheat at Countdown with this too. I'll have three consonants and four vowels please, Rachel.