For numbers, nothing beats Aflmedia.com. You have to register, and contact them via telephone to get a password, but that is relatively easy. This site is typically the first to carry news on injuries, making it essential. It also has historical data for every year of Arena. If you're curious about the exact value of "the 3" or "the 7", you can figure it out from that data. It has every stat imaginable, which can be used to evaluate anything from determining homefield advantage, to the spread differential in a loss of a starting QB.
Two other easy-access websites are Arenafootball.com, and Arenafan.com. Both of these have schedules, facts and news clippings. Arenafootball has live scores and stats for games (although the quality varies widely from game to game - sometimes up to date within 5 seconds, and rarely a game is played with no updates until it is completed).
Another site to check out is statfox.com. It has historical spreads back to 1997, although they become unreliable if you go further back than 2000.
One last place to check is AFLnet (link is on Arenafootball.com) - this carries live internet broadcast games, as well as special features. It is pay only - $65/year, but is a good way to watch another 20 or so games that aren't televised. Don Best rarely reports injuries (Bonner's injury wasn't reported), although they did pick up on Philyaw last year.
If you want to do something clever with the numbers you gather, you might take a look at Zunzun.com. This is a statistical site, and it has a great browser interface letting you analyze, graph and curve-fit any set of numbers you care to throw at it. While it is a decent starting point, it does have its limitations. I crashed it, while trying to curve-fit college NCAAF totals versus predicted yards with 20 years of data.