Found this tip via LifeHacker. Here's what you have to do...
- Type Scrabble into Wolfram Alpha and choose Computation.
- Enter the letters you have in the Word box. Use spaces for blanks.
- 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. :D