I used
www.bookmaker.com primarily for betting on UFC fights and K-1 kickboxing tournaments. The lines are pretty decent compared to some of the competition and it is VERY EASY to put money in as they take VISA.
The problem as others have said is taking money out. At one point I was up $1200 so decided I wanted to take out $1000 to get back to my starting deposit of $200. To do this you have to fax 2 pieces of id, and fax a copy of front and back of credit card and then wait 10-15 days if i remember correctly. This is even a couple months after paying initial money. To be fair, once this is done - putting in and out is probably quite simple.
I was too lazy to fax all my info - and frankly wasn't thrilled about faxing credit card/id info at same time at convenience store, since i wasn't going to do it at work ... Ended up leaving the money in and eventually got sucked into the online casino where i quickly lost all my earnings and then lost another 5G trying to win it back. I missed out on a lot of hobbying the last couple months because of my stupidity - keep this in mind anyone who is thinking of joining to make a quick buck on nice spreads. Now the only 'nice spreads' that I'm pursuing are the Asian gems of the TERB incall section =)