I like SPORTSBOOK.COM even though they have a bad reputation around these parts for stiffing / slow paying their customers. However, they have cleaned up their act and I have no complaints towards that book. They give you .10 lines on Fridays. If you're like me and know a handful of games on FRIDAY that you will be betting on for SATURDAY, you can't beat their juice.
Another favorite of mine is BODOG.COM because they're always a minute or two late in pulling their lines. I'm big on betting BAD LINES at other books, so it's critical that I have access to a book with this ability. Plus, both books take credit / check / debit cards so it's easy to get money in there.
Finally, MATCHBOOK.COM is the book that has the best lines, at .01 differential. Unfortunately, they do NOT take plastic over the internet, so a NETSPEND CARD would be your best way to deposit into their book.