e1m3. If I wanted to show someone Quake, I'd show them that (skill 3 of course.) Unbelievable how many monsters, opening walls etc. they fit in that thing. And you gotta love the lowering ceiling stuff. The moat, the zombies...
e1m4. I immediately loved the water bit, with the submerged houses. Still do. And I still didn't switch off water tinting just because of this map. And the ogre coming out of the floor... it looks like he's sawing a hole for himself to come through :-) It's so cool.
e1m6. Just a map where everything is in the right place. The moving spikes bit is cool, as is everything else about it.
Shareware quake will do, thank you :-) just like Doom, the best part is free.