Hints

Book of Beast - Riven Tips, Hints, and Walkthrough
Starts by giving you tips about playing the game, progresses to hints to help you work out problems on your own, and finally gives complete walkthroughs of all puzzles.
http://www.uq.edu.au/~e4lchan/Riven/Walkthrough.html

Calyxa's Cartography
Gallery of beautiful hand-drawn maps of Riven's islands.
http://calyxa.best.vwh.net/pearl/maps.html

Low-Spoiler Guide to Riven
Gameplay hints and two walkthroughs: one listing interesting things to try in Riven, and the other giving more explicit instructions through the game.
http://www.angelfire.com/hero/tjekanefir/riven.htm

Riven Expedition, The
A Riven walkthrough (incomplete) presented in short story form by Christopher Josephes
http://www.visi.com/~cpj1/myst/riven/

The Spoiler: Riven
Detailed Riven walkthrough including screenshots of puzzle solutions.
http://www.the-spoiler.com/ADVENTURE/Broderbund/riven.1/riven.htm

Universal Hint System Hints
Select specific questions and view hints in progressively detailed steps, from subtle nudges to full answers.
http://www.uhs-hints.com/uhsweb/riven.php