E.B.
Do everything with a "6" theme....make a 6 course dinner served at 6 pm if possible, buy him 6 gifts that represent your favorite 6 things about him &/or about your relationship, share a 6 scoop ice cream sundae, you get the idea =)
I did the gift thing years ago for our 5th anniversary and my husband was really surprised and loved it. (and don't let the cost of 6 gifts scare you because I did it on a budget...just put your thinking cap on!!) I don't remember each thing I did, but the last one was something "pretty" for me to wear....DH loved that one ; )