PvZ, Sol Survivor and Revenge of the Titans are the best i've played.

Few W3 and Sc2 maps

It is rapidly becoming the next Duke Nukem Forever.

I really like the Bloon series of Flash Tower Defense games. Nothing spectacular, but just a fun simple flash game with enough variety to make each game I play fun.

Protector IV and Cursed Treasure: Don't touch my gems

Ohhh - and of course GemCraft

Second. Also check this out: http://knucklecracker.com/

Antbuster is one of my personal favourites.

Also, seconding Cursed Treasure.

Like people said, Defense Grid, and Revenge of the Titans are solid tower defense games. I might give a shot to Sol Survivor when it's on promo.

Defense Grid and Plants vs Zombies are the best ones I've tried.

Haha, so true. The delay is all due to Microsoft and XBox certification. Gotta love it.

If you have an Xbox, you could always try Toy Soldiers. It's an interesting take on the genre, and a good bit of fun in multiplayer too (surprisingly it works well)

I like Defense Grid a lot.

For something with more depth (reasearch between maps, money carries over, etc), try Revenge of the Titans.

Not out yet but Sanctum on steam looks like it could be good.

Defense Grid and PvZ are current favorites.

I'll have to jump to something new, I've beaten all the Defense Grid maps with Gold and in some maps all the modes. I can't say I liked all the modes, Poison Core was my least favorite because all you had to do was front load your damage at the entry and exit points, anything carrying the core would get targeted first. With that said, there's a good 40 hours of fun, with the sale game and downloads I spent 9 bucks.

9 dollars and I had more fun and played longer than your average AAA title, wow. Even now that I'm "done" I still played 2 maps to kill 20 minutes this morning.

Thanks for the further posts about great games, I'll be checking out PvZ, Revenge of the Titans and all the others now.