Mpix is free - it's just like using Snapfish or Shutterfly.

You upload your pictures, select the sizes you want and type of paper (they have a metallic finish that is amazing - the photos seem to glow), and check out.
As Heidi said, though, their album sizes are limited, and I believe the page counts are too.
I am doing our wedding album as a coffee table book using Blurb.com. They let you have 400+ pages, and they have a neat 11x13 (landscape) size that's the biggest I've found so far. We did our engagement photo guest book and a small "best of" softcover wedding book through Blurb and really liked them.
They have the cheapest prices of any book-making website, but the drawback is that some people have had printing problems with them. When this happened to us with our engagement book, they corrected the problems in about 2 tries, but it can be a hassle going back and forth with customer service.