W3C Background Information
Cascading Style Sheets, Index
Cascading Style Sheets, Level 1
HTML and Style Sheets
Note: The W3C site is usually very busy. If you get no response just retry a few times.

Style Sheets: Different Flavors
Of course, Microsoft and Netscape are implementing their own versions of the standard. Netscape says Navigator 4.0 will support both CSS1 and JSSS.
Microsof't Implementation (Cascading Style Sheets)
Netscape's Implementation (JavaScript Style Sheets)

ZDNet Coverage
Unfurling Style Sheets
ZD Internet Magazine / Features
Cascading Style Sheets
PC Magazine / PC Tech: Internet Tools
Cascading Style Sheets put new style into HTML
PC Week / Jeff's Internet Adventures

Tutorials and Guides
HTML Dot Com -- Cascading Style Sheets Guide
Web Design Group -- Cascading Style Sheets
D.J. Quad's Ultimate Style Sheets Tutorial
Microsoft -- User's Guide to Style Sheets
Design Consulting -- CSS Tutorial and Quick Reference

Software: Browsers
Amaya (W3C's Testbed Browser)
Arena (Yggdrasil) Unix
Emacs-w3 (Gnuscape) Unix
Internet Explorer 3.0 (Microsoft) review
Netscape Navigator 4.0 (Preview Release) review

Software: Authoring Tools
Amaya (W3C's Testbed Browser/Authoring Tool)
DynaBase (Inso)
HomeSite 2.5 (Allaire)
HotDog Professional (Sausage Software) review
HoTaMaLe (Adobe)
HoTMetaL Intranet Publisher (SoftQuad)
Quick Site 2.0 (Delta Point)
WebMaker (Harlequin)

Examples: Sites Using Style Sheets
You won't be able to tell the difference unless you're using a style sheet-enabled browser.
City Gallery Photography Exhibits
Gareth L. Mark's Home Page
Microsoft's Example pages
Network Technology Professionals

Newsgroups
Requires access to a news server.
comp.infosystems.www.authoring.html
comp.infosystems.www.authoring.stylesheets
comp.infosystems.www.authoring.misc