Eurkea 7 is a great anime... Designs are a bit wierd, but it has solid animation, sound (If you like techno), and good-ish designs.
Break/Broken Blade is another good one unless you are talking story.
And old Mechwarrior Cartoon (American), but it has a few mechs... Not really an Anime, but MANY more people must know about it.
If you want to play a Mecha Video Game, give Armored Core a try. VERY anime-Styled.
Another, much more "realistic" game would be Chromehounds. Sadly, for both of these, you need XBox. And Chromehounds became less fun because they unpluged the servers due to lack of playing.
A THIRD game would be Lost-Planet, or that new brighter spinoff, EX troopers or something like that.