I've been working on a set of IA (information architecture) principles for the University, and in the process digging around for rules-of-thumb against which a site can be measured. Inevitably, Lou Rosenfeld has good advice, but I've also turned up a really well-considered, well-researched guide.
Lou's advice goes back to a blog post in 2004, but the basics just don't change so it's all good stuff.
Lou Rosenfeld's blog post on IA heuristics
Abby Covert is an information architect who has researched all key guidelines and heuristics published over the past 20+ years, pulled them together and rationalised them into 10 heuristic IA principles.
Her presentation is an excellent resource, and will be at the core of everything I work on in the coming months.
Abby Covert's presentation - Does it have legs? - 10 IA heuristics
Abby also wrote a blog post on how she and colleagues arrived at the 10:
IA Heuristics: a journey from the why to the how - Abby Covert