Oh, man, Yes has been my favorite band since I discovered them as a teenager back in 1983. I can give you a quick synopsis of each album:
Yes (1969): Simpler music, lots of prominent vocal harmonies. Great cover of the Beatles "Every Little Thing."
Time and a Word (1970): Similar to the first album, but with an orchestral backing. Chris Squire's bass playing becomes more prominent.
The Yes Album (1971): They begin their transition into prog-rock. First album with Steve Howe on guitar. Nearly all of this album has been on classic rock radio, and the band still plays most of it live: "Yours Is No Disgrace," "Starship Trooper," "I've Seen All Good People," "Perpetual Change."
Fragile (1972): First album with Rick Wakeman. You probably know "Roundabout." I think "Heart of the Sunrise" is one of the most astounding pieces of music they ever recorded.
Close to the Edge (1972): My favorite Yes album. Side 1 was the title track, and it's got everything from birdsong to a pipe organ solo. Side 2 includes "And You and I," probably one of their most majestic, moving anthems.
Tales From Topographic Oceans (1973): I think they went a little off track with this one. Lots of great melodies buried within long, unfocused pieces of music.
Relayer (1974): Kind of a cross between prog-rock and fusion. "The Gates of Delirium" is epic. It has some of the band's most gorgeous music, as well as some of their harshest, most aggressive moments. It's all over the place. Fabulous.
Going for the One (1977): A little lighter and less congested than the previous few albums. The title cut is a straight-on rocker, "Turn of the Century" is a lovely acoustic love ballad, and "Awaken" is one of their last great epics.
Tormato (1978): Very disjointed. Lacks direction. A scattershot approach that ends up sounding like an unfocused mess.
Drama (1980): One of their heaviest albums. Squire is extremely prominent in the mix. Trevor Horn takes over for Jon Anderson on vocals. One of their most underrated albums.
90125 (1983): The big comeback album, with "Owner of a Lonely Heart." This is where I came in.
Big Generator (1987): Rocks hard like "90125," with a few more extended pieces thrown in to try to weave in some more of the '70s feel.
Union (1991): Again, kind of a mess. Yes split into two bands, and they both get billing here as Yes, with the only common link being Jon Anderson singing for both versions.
Talk (1994): Another underrated gem. "Endless Dream" is a big, frenetic epic full of energy and emotion.
Keys to Ascension (1996): Howe and Wakeman return. Partially live, with two new studio tracks, in full-blown '70s prog style. Not bad, but they were still finding their footing.
Keys to Ascension 2 (1997): More of the same, with one live CD and one studio CD. But the playing sounds more self-assured here.
Open Your Eyes (1997): Intended to be a Squire project with Billy Sherwood, but then Wakeman left, and management wanted new material before the band went out on the road. Similar to '80s Yes, but without the great hooks and melodies and the excellent guitar playing. Frankly, not very good.
The Ladder (1999): A very laid-back, retro, AOR-style album, with one great epic piece ("Homeworld") and the rest at least enjoyable, relaxed, and unoffensive.
Magnification (2001): Their last studio album to date. This one was just Anderson, Howe, Squire, and White, with an orchestra. There's some really beautiful music on here. Very mature, self-assured playing. Definitely an overlooked gem.
If you want to get a good career overview, try "The Ultimate Yes" or the "In a Word" box set.