If you like markets, you can check out the fish market in Negombo. It is good for early mornings where you can see them bring in the catch. If you are lucky, you will be able to see some huge fish there. Early meaning 6am or earlier. Check with the locals.
If you are into ancient ruins, you get loads of it in Sigiriya, Pollonurawa and Kandy. Sigiriya is the most impressive in my opinion. But in actual fact, they all look the same after you have seen 2 or 3 sites since they are built around the same era. You may get tired of it after a while. For Dambulla, you get the Buddha statues in the cave. I have seen lots of such stuff, so I was not so impressed with the ones in Dambulla. What left a deeper impression on me was the sunset. The sun sets to the left side of the temple (as you are facing the temple) and if you get there at the right time, you may catch a good one. I got a nice reddish-orange yolk with bluish sky when I was there.
Kandy is a good place for catching the local life. So if you are into street photography, you will find it fun to wander around here. Loads of monkeys around the palace. I din enter the biggest one though. Just walked around it. Good enough.
N'Eliya was nice and cooling. A bit of European feel. Not much for scenery shots though. As for the "End of the World", I was not impressed at all. The view is not exactly to die for. Probably because I have seen better ones elsewhere. I could not see much flowers or animals on the walk in or out. Quite disappointing. Mostly just trees and bushes and that well trodden path. Super cold in the morning, but once the mist clears up, it will be hot. You may want to reconsider if you wanna go there, especially if you are thinking of lugging your camera equipment there. May not be worth the efforts.
