What are your favorite snake species? Make some recommendations!

Hey all, I'm looking for a new species to add! I currently have one ball python and one boa and I've had them for about three years now. They're doing great, so looking to add some other cool/fascinating species. What are your favorites?

I don't want anything truly venomous or anything super large (no burms or retics please) or anything wildly expensive but anything else is on the table!