Dune. (More properly known as Arrakis.) Desert planet in the novels of Frank Herbert. Pluses: It's got giant worms, Fremen (Zensunni wanderers), mind-expanding spice and lots of political intrigue, some of it plagiarised from Macchiavelli's The Prince. Minuses: No adequate explanation of how it's got a breathable atmosphere. Apparently the author once made some vague remark about the worms being the cause. Dune was made into a terrible film and a pretty good TV miniseries, with a further miniseries about the first two sequels. Yeah, Gillian will disagree about the film.
Gethen. (Informally known as Winter.) Ice age planet in a novel and subsequent stories by Ursula K. Leguin (pronounced Luh-gwan, not Luh-gwin). Pluses: The inhabitants go through "kemmer" which is a seasonal change of gender. Minuses: The book spends an awful lot of time concentrating on the rather dull politics and doesn't explore the intriguing gender issues anywhere near as much as you might expect.
Solaris. Planet covered in a sentient ocean which apparently enables it to remain stable around a double star system. Pluses: When the ocean is subjected to X-ray bombardment, it responds by creating neutrino-based facsimiles of the loved ones of the crew of the orbiting space station. The really weird bit is that the facsimiles believe they are the people they are impersonating, and it is extremely distressing to them to discover they are not. One is so distraught that she drinks liquid oxygen to kill herself, only to discover that however much it might hurt her, it won't actually kill her. Minuses: Some of the descriptions of the geographical features are not very evocative, possibly a failure of translation from the Polish. Filmed three times, and adapted (very successfully) for radio. Of the film versions, the first is not readily available, the second is by Tarkovsky and is the best science fiction ever made, and the third features George Clooney.
Skaro. Planet of the Daleks, featured in the second ever Doctor Who TV serial, which subsequently turned out to be the Doctor's first adventure in other media: Novelised in a superb children's book called Doctor Who in an Exciting Adventure with the Daleks (later renamed Doctor Who and the Daleks for brevity) by David Whitaker, and remade as a film starring Peter Cushing and Roy Castle. Pluses: The early views of the planet, and the Dalek city, are extremely atmospheric, and the Daleks have reasonable motivation - they don't just exterminate everything that moves. For 1963/4, Skaro is a remarkably varied place, compared with the "one location planet" phenomenon that is still prevalent, with a diversity of locations, life forms (including the pacifist Thals) and climate. A "TV Century 21" spinoff comic series explored Dalek history and the planet's geography. Minuses: Subsequent visits reduced the planet to the abode of the ridiculous ranting megalomaniac Davros, who got killed several times only to keep coming back spouting gibberish. It's also rather pitiful that for a space-faring TV series that is still going 50 years on, Skaro is one of a very small number of named planets that were visited by the TARDIS crew and that people can remember.
Pern. Planet of teleporting, time-travelling dragons in the series of novels by Anne McCaffrey. Pluses: It's got dragons! Minuses: I thought the stories were a bit crap. I got through the first two novels, but really, what the heck? Why would dragons be able to teleport and travel through time? Why did nobody else realise the latter until so late on?
Gor. Planet 93,000,000 miles from the Sun, but on the other side from Earth. I haven't read any of them, and don't know anybody else who has either except for a friend who died young. Pluses: They offend the more obnoxious, foaming-at-the-mouth feminists. Minuses: they offend everybody else too, including the reasonable feminists. I probably shouldn't have mentioned the books at all.
Any other contenders?