I'd suggest a pair of cockatiels. Cockatiels are very social birds and they should bond with you just fine even if they have another cockatiel buddy. I'd suggest either two females or two males, but not a male and a female. I don't like to encourage egg laying by putting a male and female together (note that a female can lay a non-fertile egg). I much perfer two cockatiels because they easily get lonely when you are away. Some kinds of bird are better left one to a cage, but I personally feel that cockatiels should always have another cockatiel buddy.