Used the Trolley tour for a one-day tour of San Diego. The route itself is really interesting, covering a number of really cool parts of San Diego (Coronado, Balboa Park and Old Town are all worth a look). The highlight though is the knowledgeable drivers/tour guides. They combine a mixture of history and humour to tell the story of San Diego.
I liked it so much I also signed up for their Seal Tour, which is also worth the money!