I suggest looking at Shore Trips. We've had great success with them.
We've got another vendor, but unfortunately we're on travel right now and I don't have access to those files. When I get back, I'll try and let you know who they were as several clients have used them and were very happy.
But this is one place where you can get a much better tour than going through the cruise line.
45 Cruises & Counting! Favorites: Paul Gauguin to Tahiti: Uniworld River Cruises in Europe; any of the Celebrity Solstice-class ships; Holland America for 12-nights in the Baltics & Russia; RCCL for 14-night Greek Isles, Turkey, & Croatia; Holland America for 14-day Alaska cruisetour; 10-night Canada/New England cruise; 21 days in Hawaii including a 7-night NCL cruise; Oceania for 25 days in Asia; & 3 months touring Europe by train. And many days spent in all-inclusive resorts!