As everyone knows, when you cast Bestow Curse, you can choose an effect different from the listed ones ("You may also invent your own curse, but it should be no more powerful than those described above."), but it may be difficult to establish what is too much powerful when dealing with things of a much varied nature.
So, is there a list of suggestions and possible curses somewhere, or things you tested in your game and seem to be alright?
Dragon Magazine had an article of alternate curses. Try there for a good reference.