I say go for the 17-55 IS. That's on my to buy list for the summer. I'm waiting for my 85 1.8 to come in the mail right now. I had the Canon 50 1.4, but didn't really like using it too often, so I sold it.
Syll is fun to play. Entangle is just plain funny, especially when it procs on first hit.
I've been liking KotL alot recently. He's damn fun to play if you build his items correctly.