Sorta "Tower Defense in Space."
Not really a short-term timewaster, but... http://www.ogame.org/
I'm on Uni2 and Uni39 as "Cbab" if anyone joins.
And Port... 
Ok, I lost a fair amount of time on that Space Game. I usually hate tower defense games, but that one was pretty fantastic.
Originally posted by: Portnoy Upgrade Complete Played this a while back... thought it was a brilliant concept just not executed all that well.
Originally posted by: The_Spectre Not really a short-term timewaster, but... http://www.ogame.org/
I'm on Uni2 and Uni39 as "Cbab" if anyone joins.
And Port...
Damn you specster...now i'm hooked! I wasn't really paying attention when I signed up so I'm in universe 3...it's not exactly fast-paced but it has a certain nerdy charm. Reminds me of a play-by-mail game I used to play, back in the 80s 
lol... I've got enough tech and resources to build battleships now, but it now takes anywhere from 5-10 hours to build ANYTHING.
And I've only been attacked once so far knocks on wood
I just 'attacked' my first planet -- an inactive account in the local system, just by way of practice. The thrill of victory!