It really depends on what you're looking for:
For a more tactical approach blended with alternate-reality Cold War geopolitics and a healthy smattering of High-school hijinks (i know...) the Full Metal Panic franchise might be for you. I'd recommend burning through/stomaching the first season to get to the really good bits (seasons 2 [Fumoffu] and 3 [The Second Raid]), which were done by Kyoani and really helped the studio settle in to its habit of belting out season winners.
"The Big O". which is essentially a detective story that happens to have city-smashing robots. Think early Batman cartoons combined with Gigantor and you wont be far off. Warning... its season-enders get a little weird. Peter Cullen (The English language voice of Optimus Prime) describes it thusly
http://www.youtube.com/watch?v=A7Nf4wfNJbA.The of course there is the Evangelion franchise (may its name be forever kept holy). You don't really 'watch' evangelion, per se, you 'experience' it. Because it has developed into a psuado meta-franchise, there is a certain order to watching it for maximum effect. Reccomended order is as follows:
Neon Genesis Evangelion (Perfect Collection) TV series
Evangelion: Death and Rebirth Summerizing Movie
The End of Evangelion Movie conclusion to above series
Evangelion Comics (Tenchi Muyo-style alternate franchises in here along with canon story)
Evangelion Renewal Project (Alternate Retelling of series. 4 movies planned, two already out)