sethgoings.com
I've run into quite a few sweet websites - which come in handy for amusement or learning. I'll keep an updated list here:

Planning/Scheduling/Group Software

Doodle: group event organizer
Unfuddle: SVN, bug tracking, project management
GitHub: Git online (public and/or private) repository hosting

Programming

Visual Representation of Sorting Algorithms
JGraphT: Java Graph Modeling/Algorithm library
Processing: Java visualization library (check out some of the demos!)
Ruby: highly dynamic, natural-to-learn, object oriented scripting language

Design / Photography

Stock Photo Exchange: where I get my banner images
Interface Lift: another high quality image site