I agree this is a tough call - there's alot of great music here. Here's my list . . .
5 - The Final Frontier. Especially the mountain-climbing sequence, beautiful.
4 - Star Trek 2009. A rousing good time.
3 - The Undiscovered Country. Excellent, especially the end sequences
2 - tie; The Search for Spock and The Wrath of Khan
1 - The Motion Picture. Really not any question here.
Sorry, I couldn't get down to five after all.