I've had good success with Riven during a recent free week. Wasn't totally enamored with Wukong when I tried him, but it's been a while. Not sure if I've ever played Ezreal.
I wound buying Janna last night on an impulse after several satisfying matches with her. Can hold her own mid lane and works as a lane support very well, while still having a respectable long-range damage output.
Came damn close to carrying my team after our top lane (Darius/Wukong vs. enemy Malphite/Wukong) were made of epic fail. Laned mid against Ryze and had him constantly on his heels (Ryze just seems to not be a good mid, at least against me) and pushed both top towers, escaped several gank attempts but then finally started falling once Malph and Wukong had like 10-15 kills under their belts thanks to the Fail Twins.
Still made a hell of a fight of it though. Took me a while to fully grasp it, but her ult is so nice because it's multi-purpose. It heals, it damages, it pushes, it blocks off lanes, it isolates enemy champs to be focused down, it can be used to throw a bad guy into your turret, it can let you escape a 5v1 chase. And Janna herself can be built aura-whore (and unlike Taric has the speed to maintain good position), she can be built straight AP, she can build CC, she can build support shield/debuffer...it's just a very versatile character and that global MS buff will always make you popular.
Once I made the realization to build a Rylai's, nobody could escape a gank. NOBODY. Although I found Janna vs. Zilean to be an awesome matchup, like something out of two kids trying to outthink each other:
Janna: "I'm faster, you're slower!"
Zilean: "Oh yeah? Ha! Now I'm faster and you're slower! And you have a timebomb on your back!"
Janna: "But your timebomb dmg is blocked by my shield! Ha! Now I knock you up in the air!"
Zilean: "No you didn't! I went back and time and sidestepped it!"
And given the low CD on all these abilities, this kind of spell-counterspell thing was going on every few seconds.