MS will not launch first, despite some claims they have made. They will relaunch the X360 as a new "cute" console, tailored to the home audience.
It might have an integrated HDD, but otherwise it'll just be a cool-running, cheap, "cute" 360.
Sony will have a PS4, with the ability to run games at 1080p smoothly, but it'll be years from now, when 1080p is commonplace. The PS3 may get a slimline model, but there's no reason for them to release a new console soon, either.
Nintendo will be the first. There's absolutely no reason for them to hold back on releasing a Wii HD -- something still less powerful than the X360, but with enough muscle to support 720p gaming. It'll be yet another upgrade of the GameCube/Wii architecture, it'll be 100% BC, and probably have an integrated HDD... probably more memory as well, since 720p games will need it.
This would be a brilliant business move by Nintendo... say in late 2010 or 2011. I hardly even use my Wii, and I would buy one in a heartbeat. You can bet all the other Wii gamers on this site would as well. Nintendo would continue to produce both the low- and high-end Wii models, and most of the shovelware would be still targetted at the low-end, where its shovel potential would reach its apex.
Wii HD... 2010 or 2011. Save your $$, because you're gonna buy one for Zelda and Mario whether you already own a Wii SD or not.