If you want to do the whole "now 21" thing then you simply must go to Trader Sam's. It is probably the best bar I have ever visited, and I have been to a TON of bars. Last time I was there another patron was having a 21st birthday and the bartenders did it up for them.
For the easiest time getting in, line up outside the doors around 10:30 to 10:45, and plan for an early lunch from their exotic menu. The bar is fun all day, but the daytime sees a lot of families with little kids. If you really want to go for the full experience, go in the late afternoon (just hang around until you see seats open up, it's annoying but eventually you'll get a spot) and plan to stay until the evening. The place fills with adults and it gets quite rowdy. If that is your thing, it's worth the pain of vulturing for seats. I really wish they would set up a host stand and hand out buzzers, but it's still totally worth it.