I have quite a few games on my phone that I would consider top notch, and some others that are good. I'll try to keep it short(ish). There's actually a few games on my phone I haven't played yet. So, I may have to update this later.
Anomaly: Warzone Earth
Super Stickman Golf
Since you asked specifically for tower defense (I've tried a bunch of them):
Hex Defense - Defensoid and Zdefense are similar TD games that are worth a look.
Angry Birds, Bejewled 2, Bouncy Mouse, ChuChu Rocket, Colorix, Cut the Rope, Edge Ex, Evac HD, Fruit Ninja, MiniSquadron, Muffin Knight, Peggle, Plants Vs Zombies, Router, Roll in the Hole, Shoot the Apple, Spirit, Stupid Zombies, Where's My Water.