I tend to like a two inner inch border and then a five inch outer border...cut at 2 1/2 inches and 5 1/2 to get that size. BUT, you need to "audition" several ideas and see what looks good to you. I also prefer my outer border to be darker than the inner, and I like both to be out of fabric that is in the main quilt top.
Now, if you really want lots of ideas, take a picture of your top so far. You will get more ideas than you know what to do with, I promise.
Dina