Tengen Toppa Gurren Lagann, Mobile Suit Gundam 00 Recommendations
Both are mechas animes with cool characters and have greats fights with nice animation. Also, Both begin with a small group of people struggling against a huge enemy army.
actually... its not VERY close to each other, but both are mecha anime. gurren lagann could have been targeted to 'younger viewers' as compared to gundam 00 (based on the degree of liveliness and typical shonen-ness :p), but tt doesnt mean its out of anyone's league.
both are also set in the future... tho those futures are drastically different. battles are fought in space (much later in gurren lagann). characters are diverse, and there's the venture of 'peace' added in both too.