Here are some good loose guidelines:
Any GSSD or OESD is worth 16 combos.
Any pair is worth 12 combos times the number of possible kickers.
Any high card is worth 16 combos times the number of possible kickers.
Any set is worth 3 combos.
Any two of one particular suit, with two already on the board, is worth 55 combos.
Any two pair is worth 9 combos.
Also, you might want to check this out. Counting combos by hand is kind of cumbersome, especially with large ranges, so I commissioned a program to do it for people. The open beta should be starting in a few days:
http://www.youtube.com/watch?v=P6fYixwfjpo