well, the recent Xenoblade and The Last Story reveals probably have me inspired, but I would say...
Baten Kaitos (Namco Bandai) Nintendo already owns Monolith, published the last game, and Namco clearly isn't going to use the IP. They could probably nab it for next to nothing, and honestly I'm a little surprised they didn't nab it when they bought Monoloith initially.
Ogre Battle Saga (Square Enix) All the mainline Ogre games debuted on Nintendo consoles, and it'd be nice to see the legacy live on (and the 8 chapter series actually complete itself). Square's obviously not interested with continuing it, so I'd LOVE to see Nintendo buy it off them, set up a new studio for Matsuno, and give us epic new DS/Wii Ogres. I think this move would actually buy Nintendo quite a bit of credibility in the JRPG community.
Seiken Densetsu / Mana (Square Enix) Another Square series that seems relegated to the sidelines, with Nintendo owning Brownie Brown and having a new relationship with Ishi's Grezzo Games, I think there's a good opportunity here. Hell, the Gooch may even want to get in on it.
Grandia (Gung Ho) Ugh, just buy it and buy GameArts too! I need a new Grandia, and I need it to be good this time! ;_;