I didn't get a writer since the project required only a reader (the cards were written elsewhere). Readers are pretty cheap, writers are surprisingly expensive.

The main things you have to look out for are coercivity and tracks. Magnetic stripe cards come in both high-coercivity and low-coercivity (HiCo and LoCo). This is a bigger issue if you're doing writing, I believe most readers are compatible with both. There are typically 3 tracks of data available, so you'll also want a reader (or writer!) that can access all three.

The model I got could be programmed through a Windows only utility and that seemed pretty standard, so at least make sure you have a virtual machine with Windows on it. You'll need to program it to tell how to interact (as a keyboard is easiest) and if you want to fiddle with the tracks.