It depends on what you want to play. My last 1.350 champion was Twisted Fate, and I loved him -- but he's ranged, and you apparently already got ranged. First, what you should see is if there are no 450 champions you want: remember that with the cost of a single tier 1 champion you can get three tier 0 ones (correct me if tier 1 isn't IP 1.350), and there are some interesting ones in the cheaper category.
If you want melee, I can guarantee you that Dr. Mundo is fun. Why? Because Mundo does what he pleases.
Nasus is great and pretty balanced: you can tank, control lanes, solo mid, push and even net kills with him. Good survivability, and his Siphoning Strike really makes farming a charm.
Sion's interesting, too: I never played him myself, but my roommate has been using him for the past week, and he doesn't die more than once in matches, even if we lose.
Good luck picking, take my advice concerning the 450 IP champions in consideration before purchasing a 1.350 champion.