Sony published a mysterious teaser on the SonyStyle home page for a new product that will be announced on Monday July 14th, 9pm EST.

Update:
Sony Mystery Gadgets revealed

The image used shows a green lit power button somewhat reminding me on the Xbox 360 power button.
The brief tag lines talk about style, performance and mobility redefined.
I could imagine Sony is introducing an Intel Atom based netbook. The three tag lines would fit to such a product. The big power button is a bit confusing, but this might just be a close-up of a small button.
See the Sony teaser on the SonyStyle site. (Thanks Brian).