DS - Professor Layton and the Diabolical Box (August 24)
The Professor Layton games have a lot going for them. The environment is unique (including the artwork AND some amazing music!) and well done and the puzzles are challenging. This is the second installment in the series (after Professor Layton and the Curious Village which came out in Spring of 2008).
Wii - Muramasa: The Demon Blade (September 8)
Something tells me this is going to be a sleeper hit. I haven't seen a lot on it, but it's clearly bringing a lot to the table: unique artwork, a story inspired by Japanese history, and some interesting gameplay elements. (basically, will it repeat the "success" of Okami?)
DS - Kingdom Hearts: 358/2 Days (Beware - That's a gameplay-only clip) (September 29)
Need I say anything? Of course, unlike the two games listed above, you need to have played the other Kingdom Hearts games to fully appreciate this one: Kingdom Hearts 1, KH: Chain of Memories and KH 2. All are excellent games offering an attractive blend of Disney environments, Final Fantasy characters, anime-style graphics and gameplay, and a pretty interesting (and now well-developed) story!