Willowware has released it's Audit Trails software for Dynamics GP starting at an incredibly low $599. I haven't demoed the software but it looks good, including a web based reporting interface with the source code. Additionally it use a client license so you can audit as many servers as you like with one client license. Like other auditing software it works at the SQL level and so it's not dependent on GP but could be used with Dynamics NAV, SL, AX, CRM and conceivably other products.
There is a trial download and once I get past all my year end stuff (and there's a lot of it) I'll demo it and add a review to our new Module Review section. In the mean time, check it out and you'll be able to add your review as well.
Clarification, Willowware is partnering with ApexSQL to offer their Audit Trails software to the GP community for $599.