None right now, none in the next 3–5 years I would say.
Xbox is looking to hold onto market with its 360 (and with 50% failure rate, trust me, they can’t afford to even THINK about the next generation) by introducing the Natal features via an additional set you purchase, likely.
PlayStation is just releasing their PS3 Slim, they have been simply too expensive to reproduce its dominance of the market as it did with the PS2. The slim will help them save money on their cost of unit, but by far they are still the most expensive and smallest revenue of the three, so they’re not looking to make a new console yet at all. Their PSP is doing quite nicely though, and the update they’ve made to that will help immensely.
Nintendo is doing just fine with the Wii and the DS. While it’s not as much of a hardcore console as the Gamecube was, it is still quite suitable, as sales of Galaxy and Smash Bros etc show! More importantly, Nintendo has always made a profit off of their console from Day 1, which was untrue for MS and Sony. So Nintendo doesn’t really need to innovate a new console at this time.
I think we will be seeing more micro updates to the consoles for quite a number of years before we start hearing of the next units in development. Plus there are other competitors to the video game landscape which may be causing the companies to hesitate in inventing a next generation which may be useless (I’m talking about OnLive and other “streaming media options” where having a console may never be needed).