With the recent sale on Quake, i guess a lot of people will get it. Undoubtedly, the next thing you will do is get a decent sourceport for it. I've read several threads, and some list a decent variety of those, the most popular being Dark Places (for the graphical enhancements I guess), followed by ezquake, qrack and some others.
However, I'd like to recommend another sourceport (or engine, as the author calls it). It is UQE Quake (Ultimate Quake Engine for Quake). What I like of this port is that it keeps a lot of the original feel of the game itself. On the graphics department, it supports some kind of post processing, but I feel the "Classic Rendering Mode" to be the best part.
Quake is a great game on itself, and I think it should be experienced like it was originally (yes, pixels included), at least 1 chapter, so you can appreciate the game and the technology that fuels it better. Yes, you can disable all the bells and whistles on Dark Places, but to achieve that, you have to fiddle with a lot of menus, particle options, rendering options and what-not. And even then, I never like the final result or the feel.
Finally UQE comes with a nice support for high resolution textures, external BSP textures, colored lightmaps (get some colored lighting for a better ambience ;)), MDL skins and OGG vorbis, mp3 or WAV music files (no need to mount the cd image to get music in game). Finally, the port has the best "no input lag" vsync of all the sourceports that I have tested.
For those interested, all you need is the game's .PAK's. Here is the link to the author's page: http://www.korvinkorax.com/games/ultimate-quake-engine
Anyway, no matter what your sourceport of choice is, I really hope you enjoy Quake as much as I did when it was released (and pretty much every time i get to replay it :)). Happy Ogre hunting!