Hmm, have you tried:

Trundle and Udyr are great duelists and splitpushers later in the game and can become very durable. They both work very well with CDR and their CC, while somewhat limited can be very good in certain situations [i.e. Trundle pillar blocking a jungle path, Udyr stun letting him stay on enemies]. Their mobility isn't as great as some champions, but Udyr has a very nice, constant movement speed boost and Trundle's is over a significant area with a nice steroid (especially in the jungle). They deal a lot of consistent damage, so they are great for taking objectives.
Jax is another good splitpusher with an AoE stun, a defensive steroid, and a lot of damage. He is very strong late game, both in teamfights and splitpushing with good burst, sustained damage and mobility,
Riven requires quite a bit of skill and game knowledge to perform with optimally, moreso than most champions, but she can be very flexible when played well. High burst damage, decent CC, high mobility (especially with CDR), and decent survivability through her shield and lifesteal.
Hecarim scales very well with items (especially CDR and Sheen), can potentially heal a lot in fights (through his W), can initiate or disrupt teamfights, and is pretty mobile (E and R, though the cooldowns are pretty long).
Irelia is typically stronger in the mid game than late game in my experience, but she's also a good option. CDR is great for mobility, CC, and W uptime. Her Q can let her dash between minions to chase or juke (kill them for a reset) or to stick on enemy champions in a fight. And she only really needs Trinity Force to let her assassinate squishies for most of the game, so she can build defensively quite easily.