I've referred to AHL roster limits in passing before, but never gathered it all into one post, so let's do that now, as people are still looking for the information.
There is neither a salary cap nor roster limit in the AHL. There is a limit to the playing roster, meaning how many players take the ice in a given night, but teams can keep as many on the payroll as they like. Relatedly, there is also no IR (injured reserve) in the AHL. The need for an IR comes out of roster limits, so given no roster limit, there's no need for a special shelf for injured players. (And because of this, AHL teams give virtually no information about injuries. They don't need to explain why someone is sitting, so naturally they usually don't.)
Why is there no salary cap in the AHL? Salary caps are usually done for parity reasons, but there's no real need for one in this case, given that most of the players are on NHL deals that limit the amount they can make in the minors. The rule about how many veterans a team can play in a game helps keep parity as well. The AHL refers to this as its "development rule":
Of the 18 skaters (not counting two goaltenders) that teams may dress for a regular-season game, at least 13 must be qualified as "development players." Of those 13, 12 must have played in 260 or fewer professional games (including AHL, NHL, IHL and European elite leagues), and one must have played in 320 or fewer professional games.
All calculations for development status are based on regular-season totals as of the start of the season.
Eighteen skaters a side for 2008-09 is a change from 17 skaters in previous seasons, and brings it in line with the NHL.
There are usually a few players in the AHL that make over $1 million, but most make around $50,000 or so.