Google

Tons of smart people. Arguably the most interesting problems in computer science are being tackled on a daily basis -- certainly at an unparalleled scale.

Different product areas have different cultures, so it's hard to generalize about the company as a whole, but I don't think any other company offers as good a combination of interesting projects, great benefits and compensation, smart co-workers, and good culture.

It is worth noting that your experience can vary a lot depending on your product area and manager.

The company has gone a bit overboard in adding multiple levels of management in recent years, and the organization feels more top-down than in the past, but neither aspect is too severe. Be prepared for a long commute if you want to live anywhere affordable or interesting. There is an astonishing lack of diversity in political viewpoints; if your heroes are not Barack Obama, Nancy Pelosi, and Paul Krugman, then don't even think about engaging in a political discussion with your peers (in person or on any internal mailing lists).

Break down the silos among different projects and different product areas.