We are using the GX420d model from Zebra. You can order these with Parallel port, Ethernet, Wi-Fi or BlueTooth and they also have a USB port. I've used them from OS X and Linux without any problems. There are drivers for the thing, but you can even print using HTTP, POP3 (!) or connect to the printer over TCP and send your raw commands through that.
It took me about a day to figure out how they work, but the printer language is quite easy to understand. Documentation is well done, but getting access to the docs is not so easy. The Zebra tech support is quite helpful though, so you can always ask them.