We did the hop on/off trolley tour with Old Town Trolley when we were there a couple of weeks ago. Our first driver was a bit over the top, but we liked the second one we had (we jumped off at the Southern Most Point and then back on after we took a picture).
We also did the Little White House. My DH and I loved the Little White House but my kids just tolerated it. But even though they don't appreciate all the places we drag them to, we still do it because I think it's important to expose them to history. Maybe they will appreciate it some day.
Finally, we walked from the Little White House to Kermits to get our chocolate dipped Key Lime Pie. I had the strawberry dipped in white chocolate which was very, very good.
Most of the main stuff to do (Little White House, Hemmingway House, Duval Street, Aquarium, Shipwreck Museum, etc) is within walking distance of Mallory Square where they drop you off so it would be easy to do on your own too.