Do you know of any good, credible GMAT study websites?

I need to study for the GMAT. I’d like to do it online because the test is computer based now. I’m really worried about the quality of the website because while I don’t mind paying to belong, I don’t want to get caught up in something like this: http://www.businessweek.com/bschools/content/jun2008/bs20080627_391632.htm?campaign_id=rss_daily

(Short version: the site used questions still currently in use to help students study. It’s not clear if everyone knew the questions were “live” and I feel like there is a good chance some students had no idea. I don’t want to be a student that has no idea.)