I keep these bookmarks open in Opera tabs all the time for quick reference:
Zzappers Best of ZSH Tips - Holy, zsh is so amazing, I don't think I'll ever use all the features, but it's so nice knowing that they're there, if you need them.
A (Re)-Introduction to JavaScript - Now that I have JavaScript: The Definitive Guide this is probably not quite as necessary, still it's a great reference
19 Rails Tricks Most Rails Coders Don't Know
Developer Notes for prototype.js by Sergio Pereira
The Ruby on Rails API - Actually I cache a local version, for speed and grep-ability.
Amazon EC2 Getting Started - EC2 (and services like it) are totally the future. Having your own datacenter and servers is so last century.