If you're thinking about going to the beach, I recommend San Andres, Colombia (beautiful Island, try to go to Decameron El Isleño hotel, we went there this February - pic here) and it was AMAZING, we fell in love with this Island!. Personally, FH and I have our hearts set on going waaaay south, to Ushuaia, Argentina (known as "the end of the world" since it's truly the last city on the continent), it has obviously a cold weather, and that's one of the main reasons we want to go (we have an extremely tropical weather)
I haven't been to Peru for Costa Rica is beautiful!! Check out the Rio Celeste!! It's amazing it's actually blue caused by 2 streams coming together which they each have different properties that when they mix it turns the water blue!! It's in the middle of the rain forest and you need to hike I suggest hiring a guide which is what we did!!
We also rented a treehouse on the beach in Samara beach!!
There are tons of mosquitoes though I came back with 30 bite on my leg! LOL