Tourism in Sri Lanka is on the rise and it's especially popular among beginners and people from countries with no waves of crappy surf.
Arugam Bay is the most famous wave, but I stayed in the South (near Galle) and didn't surf there.
There's a lot of good breaks (nothing fancy) around. I went there 7 years ago and stayed in a hotel right on the beach (Koggala). It was a good beach break with no one out; the only guy out there was an Aussie surfer.
I went exploring a few times and saw some good waves. One of them was a left pointbreak perfect for SUP (I think it was Midigama). I also surfed a good pointbreak in Mirissa.
So, don't expect anything fancy like the Maldives or Indonesia, but there are some fun breaks around.
@Carles RSPro I think August is a good season. I went there during Christmas and there wasn't any significant activity in the Indian Ocean, but in August there's a lot of storms down South that bring long period swell.