Garmin has done well for me on mac for several years. I just bought an Edge to replace my ancient GPS3+. When attached to the computer via usb cable it shows up as a usb flash drive, and the files are directly accessible. They're also in an open source standard xml, published and available on garmin's web site. So they're compatible with any gps software you can find. (or write... which I did!)
Additionally, there's two sets of free software you can download from garmin that work shockingly well on the mac. One is for training (since the Edge is a trainer, I use it as a bike computer / gps) and the other is more of a traditional GPS software, managing routes and waypoints. It uses a web browser plugin (FF/safari) that integrates seamlessly with your gps when plugged in, and is reminiscent of google maps. It also exchanges with your online profile at garmin and can be used to exchange / publish routes and workouts etc.
Garmin does what all the others do though, sells you map upgrades for things like waterways and other countries etc but the prices aren't out of line.
The new edge does NOT have NMEA serial output unfortunately. This allowed me to write software that sent live GPS position information from my 3+ to my computer. (combined with downloaded satellite imagery, made for some interesting james-bond-ish stuff) If you need that capability, be sure what you get supports NMEA.
