Try this:

  =iferror(vlookup(C2,Sheet2!A$1:B$6,2,FALSE),"")

[Here's an example][1].

Some notes:

- Put the formula in the cell you want to fill
- C2 refers to the value you're using to look up in the array
- When entering the array range, make sure to put in `$` before the row numbers, otherwise the range will be dynamic, not fixed.
- If you add more categories, you'll need to update the formula on Sheet1


  [1]: https://docs.google.com/spreadsheet/ccc?key=0AhUKe_nNHFlTdHkyQWVGVjNKTlVUV2N4aXFBcE41N0E&usp=sharing