Why the Lucky Stiff's guide is a classic and must read (gotta love the Chunky Bacon!). Here are some other recommendations:
Note: These guides are for Ruby on Rails (rather than just plain Ruby), the most popular way to use Ruby for web developoment.
-- from Rails' creator(s)
-- from Geoffrey Grosenbach (give TopFunky a shout-out for me).
I have personally used all of the resources available on these sites and I think they are a great starting point.