The Financial Times Germany (German) published a story saying that Microsoft will cut the price for the Xbox 360 on Monday across Europe.

Update:
Xbox 360 Price-cut Official

The Xbox 360 Arcade is supposed to sell for only 199 Euro instead of 280 Euro. A 199 Euro Xbox 360 would be 50 Euro cheaper than a Nintendo Wii.

The Xbox 360 Pro would also see a price-cut to 299 Euro (349 Euro now).
If Microsoft is indeed cutting the Xbox 360 prices in Europe on Monday, I would not see a reason why they would not do the same in the United States. The Xbox 360 Arcade sells currently for $280. A price cut to $199 would have for sure a greater sales effect in the U.S., as Nintendo is still not able to keep the Wii in stock at major retailers to give consumers a chance to buy it at the MSRP of $249. Instead the prices for a Wii console are still close to $400. An Xbox 360 Arcade would just be half that price after the rumored price-cut.

Microsoft could win some time with the price-cut to prepare for a new generation of Xbox 360 consoles with integrated Blu-ray drives. Microsoft is supposed to be in talks with Sony about licensing Blu-ray for the Xbox 360.