Over the last 3 years, NFL Draft Countdown has been the most accurate among mock drafts. Rick Gosselin of the Dallas Morning News is #2 and not far behind. Gosselin's has proven so accurate because for whatever reason he calls teams in the weeks leading up to the draft and they seem to tell him who they are drafting.
Draft Countdown is a very good site. But in the near future, it's probably going to go the route as all draft sites are going, and become a pay site.
If you truly want to immerse yourself into the NFL Draft, not forking up some dough is pretty much impossible. You'll be missing out on a lot of info, and basically have to hope that people on message boards like these (that do pay) pass along the info they find.
And IMO (although you may consider me biased, since I am a Sr. Contributor to the site), if you want to get the most bang for your buck, you should suscribe to The Huddle Report
. Only $10 for a year, and you pretty much get everything (if not more) than you would get at most other sites that charge you $25 or $30 for an entire year.
I am currently subscribed to these sites:
The Huddle Report ($10)
NFL Draft Scout ($25) - Their news and position rankings I believe are pretty accurate to what NFL teams are thinking.
NFL Draft Experts @ Scout.com ($50) - Why I pay that much I'm not sure. It's probably not worth it but I do like the fact that they have available player profiles in October & November (well before anyone else I'm aware of) and their combine/All-star game coverage IMO is second to none.
But in all honesty, because of my affiliation with The Huddle Report, I don't pay for the first two. But in essence, I'm investing $85 into a whole year's worth of information, but when you consider it to be only a quarter a day, it's not that bad, although it probably really works out to be closer to $0.40 or $0.50 a day, because between May and August/September, there isn't a lot of info to go around, so you're really only getting about 6 or 7 good months of coverage and the other 5-6 months aren't a lot.