Houses of the Holy is my favorite Zeppelin album. No one I have ever met agrees with me but it has some truly amazing songs.
This one in particular is the reason I started listening to Led Zeppelin when I was under the hill.
White Summer was played at Zeppelin concerts through 1968-1970 and was brought back for the legendary tour of '77, Knebworth '79 and Tour Over Europe 1980 (which was the last Led Zeppelin tour before John Bonham died in September 1980). Over the Hills and Far Away emerged from a 20 minute instrumental session of White Summer/Black Mountainside that Jimmy Page recorded at Headley Grange in 1974. Over the Hills and Far Away was "spun off" according to Page from this session.
I've been listening to classic rock my whole life, well before it became classic, and I'd still say this is my favorite album ever from start to finish. Granted, Zeppelin is my favorite band and I like all their music, this is just still what does it most for me. Every song.
Achille's Last Stand is actually an amazing song. It's probably the heaviest song that Zeppelin ever made. The album doesn't really flow that well in my opinion but it at least starts with a bang.
Nobody's Fault But Mine is good too.