True, with a bit of time you can bounce between classes for a fleshed out setup. Multiplayer with randoms can also mean your setup gets destroyed by some random (usually a knight) such is the way of pugs these days where being a dick is perceived as amusing for all.

Ive got a couple more Ive found in my Steam library I found promising enough to buy on sale but havent had a chance to play yet:

Defense Technica
Radiant Defense

I heard so much good about Orks Must Die that I bought that series on sale but havent played. Im not real keen on mixing 1st or 3rd person action with my TD but one of these days Ill try it.

Deathtrap looked like a great TD game to me. I was so excited watching the trailer UNTIL I saw it had a character you have to control to help kill the enemies. Seems TD games think they need to mix genres into the mix, and I disagree. This trend needs to stop IMO. There are plenty of games I could play if I want to control a hero in an action rpg or whatever.

Orcs Must Die is a lot of fun, sorta half action and half TD.

There's also Mars Tower Defense which is great and free (browser game, but it's as if tower defense was put on a NES cartridge).

Plants vs Zombies GOTY has to be the most fun tower defense game i have ever touched! Give it a go, you won't regret it! Avoid the steam version, though, it is unstable and full of issues. As much as i hate to recommend something bought off from EA, that's where you should get it, alas... On Origin, it was given out for free, quite some time ago.

Great list!

I'd suggest GemCraft Labyrinth for the Online section.

Many of the elements in GemCraft: Chasing Shadows appeared here before but there are enough differences to make it worthy of playing. I particularly enjoyed that many maps allowed for more freedom at controlling the path of the bugs. The "boss" maps were interesting too.

Plenty of hours invested in that game.

I recall downloading gemcraft before as swf files... are there specific versions that are online-only? Or not? I don't remember, honestly I never quite beat the first game and had my fill of it.

I noticed Infested Planet is on sale over at Steam and picked it up. Not sure how much Tower Defense it is really but thats one of the tags. Im about to find out because I just installed this one.

Also picked up Terrorhedron. Its only a $2 game but it looks pretty interesting and polished to me. For that price its worth a try.

I almost forgot Super Sanctum TD I got last week but havent tried yet. It looks like a mobile or tablet game but its much more old school TD than Sanctum 1 or 2. Its just a $4 game but I picked it up on sale.

I would just like give another plus for these games:
- Defense Grid
- Kingdom Rush and Kingdom Rush: Frontiers

I would also recommend Tower Wars and Shad'O

Also Creeper World 3 and Particle Fleet: Emergence.

Also Revenge of the Titans from Puppygames is also good.