It started with Flash Element TD.
Then there was Desktop Tower Defense
The creators behind both of those games have combined forces to create Casual Collective, a game site that includes support for social communication along with new games. It might be worth a look.
As a side note, this post marks the first time in the history of my blog that I posted every single day. I came close to doing it in September 2002, missing only one day (the first Tuesday of the month). The only way I managed to do it this month was by scheduling posts in advance. At times I had a whole week scheduled out. It doesn’t work too well for timely posts, but it works great for evergreen entries.