I would encourage you not to do a turnround if you have the time - Sri Lanka is a beautiful place, and the people are extremely friendly. I had a great week there with my GF (I was goingto say "recently" but I discover it was 18 months ago!) up in the hill country around Kandy, Nurawa Eliya and Ella. It isn't "big sight" tourism but it is a very interesting country to see. (It is also rather touching to see how proud the locals are of some of the temples which, particularly if you have just come from Bangkok, are, frankly, fairly non-descript - this adds to the charm of the place rather than detracts from it IMO).

We worked with Malik at Dream Vacations ( http://www.tourslanka.com ) to put together a customised version of one of their tours and it all went very well. They have an emphasis on using ecologically sound suppliers. My GF particularly enjoyed her time at the Ella Adventure Park, which was very well (and safely) run. Dream Vacations have expanded the range of what they do considerably in the past year.

Also try to take the journey from the Hill Country back to Colombo on the train if you can - this is always a great way to see a country.