You could check out Song summoner: Encore. I enjoyed but it seems I'mi n the minority there. Though it is the most FF: Tactics-like game on the appstore. Also a good (if slightly different) suggestion is Battle for wesnoth. It's more of a tbs than a tactics game though I highly recommend for the massive amount of content it has.
There is also Uniwar which is more of a turnbased Advanced Wars-esque game. As far as FF Tactics your best bet would definitely be Song Summoner. It was fun, and I liked it too.
Ooh, I just thought of another one - Laser Squad (by the same guys as X-Com) is a free download within Commodore 64 (which is also free) It's old and crusty, but it's a solid tactical squad game, especially for free.
I thought Summoner was amazing, and FF Tactics used to be one of my favorite games. But I'd take a look at Rebirth Of Fortune. At the moment, my iPod is broken or I'd have downloaded it already, but it seems to be a copy of FF Tactics' play style and graphic style, but with little to no store. If you're simply looking for battles, it looks pretty great haha. However, Summoner will always be #1 in my book (iPod tactics wise )