For Jimmy Page, the most famous alternate tuning is an Indian-based structure, which gives the guitar a sitar-like sound.  Page first learned it in 1966, when Al Stewart taught him to play "Black Waterside", (by folk musician Bert Jansch).  The next Yardbirds' album ("Little Games" released in 1967) featured Page's "White Summer" in this D modal tuning.  The first Zeppelin LP would then include  "Black Mountain Side", similar to Jansch's arrangement.  "Kashmir" and later "Midnight Moonlight" (a left-over song from the Zep era called "Swan Song") would also feature this tuning.

The Led Zeppelin III era contained a stronger focus on acoustic sounds.  This folk tuning was used on "Friends".   Also recorded during this period (and in the same tuning) was the instrumental "Bron-Yr-Aur" (later released on "Physical Graffiti") and "Poor Tom" (finally released on "Coda" in 1982).

An open C tuning was used for the slide blues "Hat's Off to (Roy) Harper" in 1970.

Open G was used by Page on several songs including: "Black Country Woman" &  "Going to California".  Tune it a semi-tone down for the studio version of "That's The Way".

Simply drop the 6th string to a D for "Moby Dick" and "Ten Years Gone".

Probably the most "pretty" chords were achieved with these tunings for the Rain Song, which raises a step for the live performance.