Google

Google was founded based on the ideals of having a comfortable work environment, and it shows.

Free food and tons and tons of benefits are available. Other examples include free bikes, on-site gyms and massages, free shuttle buses around the Bay Area, and even free co-op cars for employees who bike to work.

Aside from the benefits, the people at Google are also what makes it stand out: you'll constantly be in close proximity to some of the smartest people (albeit some are weird) around. Of course, since there are so many projects, the work quality can vary, but I was extremely happy with my assigned work when I was there as an intern.

Since there are so many projects going on at Google, you may be hired and work on something not so interesting. Of course, there are opportunities to change your team, but it may take a while.

Similarly, since some projects are experimental, it's possible that your project is shut down and you're moved to something else.

Though not technically a 'downside', the only reason I am not returning to Google is because of the lack of hiring right now. I was interviewed and offered a full-time job; however, it wasn't in the type of work that I wanted to do. This is also the case with a handful of other interns that I know.

I didn't deal with senior management enough to have an opinion.