Sometimes technical, sometimes not, never a kitty

SQL Server:
Introducing SQL Internals Viewer (via Jason Haley - sweet tool!)

XML:
Avoid the dangers of XPath injection (also via Jason Haley via Frank Kelly)

SubSonic:
SubSonic: SonicCast #1 Is Up
SubSonic: SonicCast #2 Is Up - All About Paging
(umm, dude, 2 in 24 hours, I can't watch them this fast)

TDD:
Getting with it: Test-Driven Development

PDF:
Featured Windows Download: Edit PDF files for free with PDFill
CC Licensed PDF Documents from any Application

Blogging:
BlogEngine.NET: Creating Themes Webcast (via DotNetKicks)
Making Your Blog Printable (via Jason Haley)

Second Life:
Dante's Virtual Inferno : Second Life breathes new life into classic literature
(I never thought of the playground-as-a-learning-tool angle, but this has more promise than even a virtual economy)