I was bitten by the 6502 bug somewhat recently as well. I got rid of most of my bookmarks when I dropped it, but let me see what I can dig up.
Wiki full of articles from the golden days of the C64 demoscene, discussing a lot of essential 6502 routines (pretty much everything you need to do fast math), code reviews for interesting codebases (like Rob Hubbard's music routine), general program structuring advice, etc.
http://codebase64.org/doku.php
The nesdev forums are home to a lot of NES homebrew projects. There's a lot of great discussion micro-optimizations there, along with some NES-specific stuff that you probably aren't interested in. If you are interested in deving for a console, where lots of ROM + tiny RAM is a significantly different experience from deving for something with 64k RAM and a disk, you'll especially appreciate their discussions of game program structure. Writing a program that runs efficiently out of ROM can be a bit of a challenge, as a lot of the techniques that are natural on a computer aren't available to you (when you've only got 2k or 8k of RAM to work with, you really need to be thrifty with runtime code generation, but you can still get away with it if you're clever).
http://forums.nesdev.com/
Obviously there is 6502.org, full of links, articles, and an informative (and surprisingly active!) forum.
Whatever assembler you're using, make sure you learn your way around its macro syntax. Good macros are invaluable in pure assembly language programming.
I'll post any other links if I remember them.