Revenge Of The Titans is $7.47 (
$14.95) at Direct2Drive (US Only) if you use the coupon code REVENGE at checkout. Works for the Mac version too. Unfortunately the coupon only appears to work on the US site. I got this coupon from their email list so there might be a different one for the UK.
ROTT is an indie tower defense/RTS hybrid type of game.
You can try it free for an hour at D2D or you can download the demo direct from the devs.
It doesn’t have a metascore yet but it has a 7.6/10 user score at Metacritic.