Android users everywhere are all talking about Ingress. It's a cool location based MMO sci-fi game where you secure portals to help alter the course of human history. The back story is all at the Niantic Project website, and it's quite the puzzle itself to get it all sorted. The short version -- it's fun, it gets you exploring, and it's addictive.
It's also invite-only for now, and that's always a bummer. There's a couple ways to get an invite. The first way is to sign up for one at the Ingress portal site. They're metering them out, but that's where most people that are playing today got theirs.
The second way is to jump on Google+ and add these four folks from Niantic to your circles:
Read what they post, because they are the people who can override things and hand out invites -- and they often do. Try to catch their eye with cool artwork or stories with an Ingress theme, and mark your post with the #ingressinvite hashtag, and maybe even mention them so your post gets seen.
Finally, you can get an invite from a friend who has scored a handful from the game. Word is that you can get invites to pass out once you reach a certain level (between 2 and 3) but nobody is 100-percent sure.
What I am 100-percent sure of is that I don't have any. Instead of pummeling my inbox for one, try the tactics above. It's fun enough to work for.