Probably the most important publications in Runequest / Glorantha in years are the new Cults of Runequest books.
There will be 11 books in total, listed here in no particular order: Prosopaedia, Lightbringers, Earth, Mythology, Darkness, Water, Solar, Lords of Terror, Horned God, Invisible God, Lunar Way. Those in bold are already available. The Mythology book is coming in October.
The first one was the Prosopaedia, published first simply, I think, because it was ready first. On its own it's not that great a resource for players - though may be for GMs because it's effectively a summary of what was to follow in the individual pantheon books.
The Lightbringers and Earth pantheon books are a different kettle of fish. Containing, between them, 35 cults, including those most commonly used by players of Sartarite and Praxian focused games, and adding the same kind of detail as the ground-breaking Cults of Prax from all the way back in 1979.
One of the great things about the cults books though, are the cults which players don't tend to play. These are not just a bunch of cool new spells and skills for PCs to bring to bear, they're part of the monumental world-building of Glorantha. Some of these gods exist not to be be part of a party's toolset but simply because they are interwoven into the mythology of Glorantha and deserve to be present.
All available from Chaosium, of course, as print (with free PDF) and also from local game shops which are part of the Bits and Mortar initiative.
If you run a game, or play a game, based in Sartar or Prax, I'd say these books are pretty close to being essential to deepen your understanding of the cults of Glorantha.
