We always stop at the Crow's Nest Marina at the Venice inlet. Docking can be tricky when the tide is coming or going, but the staff is great at helping with directions and line handling.
We stop here mainly for the restaurant and tap beer, but the boat and people watching are also entertaining. The sunsets are fantastic. The park across the inlet fills up with people to watch the sun slip into the Gulf, and they put on a fireworks show on certain nights as well.
Another stop is on the Manatee River and is a Safe Harbor Marina, Regatta Pointe Marina. The Marina is a typical Marina, but the restaurant, the River House, is located on the end of the pier, giving diners a great view of the river, boat traffic, and a beautiful sunset. There is also an outside pub called the Snook, I believe, where you can just have docktails and/ or a bite to eat. They also have free bicycles for use by transients and a Publix a few blocks away.
Bradenton Beach Marina is right on the main shopping area of Anna Maria where you catch the shuttle that goes up and down the main road giving you access to all of the great restaurants, little shops, beaches, etc. The only problem is that the marina is very popular, which makes it hard to get a slip.
Hope this helps.
Terry