Been using Hulu for a while (about 6-8 months). It's great. It's an online service that is free that lets you watch Fox and NBC programming right there on the site (it's co-owned by those two companies). It has links to programming from ABC and CBS as well, but they open in different browser window.

Video quality is good. Episodes, in general, have four to five :30 mid-rolls, so you probably see less ads watching it on Hulu than you would watching it on TV. But you can't fast-forward through them.