If you’re on a budget there’s a fairly cool hostel called Love Lane Inn in Georgetown run by a helpful and friendly Taiwanese guy off Chulia Street. If you stay there most people you meet there though will be doing visa runs from Thailand.
I would have liked to have seen the monkey beach while I was there. I would give the snake temple a miss. There are two snakes in the temple.
The buddhist temples are worth checking out due to their sheer size. If you can get inside a mosque probably also worth checking out.
The tropical fruit farm may be of interest.
Fort Cornwallis is interesting from a historical perspective. The person I went with was bored silly though. The cannon there is believed to be a fertility cannon.
Going up Penang Hill looks like it could be worthwhile. I’ve been a little way up the hill.