25 Things You Should Know About Worldbuilding by Chuck Wendig
The 7 Deadly Sins of World Building. Read the comments also.
Five Foundations on World Building by author Malindo Lo.
Writing Fantasy Tools & Techniques (World Building) by author Brent Weeks.
Writers Working With Louise Cusack. A guest author Rowena Cory Daniells talks world building.
Building Blueheart. A water world case study by author Alison Sinclair.
Science Fiction and Fantasy Writers of America
Squidoo Fantasy World Building
World Generator (building planets with the press of a button)
Strange Maps (lots of different real world maps to inspire)
Primitive Ways (if your world isn’t advanced)
Climatology (figuring out world climate in detail)
And finally, here’s an entire blog about Worldbuilding: Worldbuilding Rules!