We're not too sure if this is all too credible, but Achievement Hunter seems to have a release date for Mega Man 9 (this seems to only pertains to the Xbox 360's Live Arcade). The source claims September 24th, 2008 is the date Mega Man 9 hits the Live Arcade. Again, we're not too sure if this is correct, yet. But a possible date is better than no date at all. We have no clue what this means for the PSN and WiiWare's releases, but it is important to note that Sept. 24th falls on a Wednesday - The day Microsoft updates with new arcade games.
Thanks goes to new forum member Flamedramon for the link.
Source: Achievement Hunter - Megaman 9