Folk I know

Welford Observatory - updates from Welford observatory including many good pics
Alec MacKinnon - academia done right

Things I like

www.slackware.com - the oldest surviving linux distro that I use day to day
www.linuxquestions.org - the slackware forum is particularly friendly
www.clivejames.com - I agree with much of what he says, and even when I don't, I like the way he says it
From our own correspondent - frustrated by regular news? Try this.
android - An open source OS that I use everyday.

Historical (mainly Scottish)

RCAHMS - The Royal Commission for Ancient and Historical Monuments of Scotland. Images and info.
SCRAN - A huge collection of images of Scotland with text information too.
NLS - National Library of Scotland. Treasure trove of information, especially for old maps.