A bunch of good and easy-to-implement tips. Smashing Magazine does a great job so if you like this article, check out some of their other stuff.
Update: Here's another good article from Smashing Magazine "Data Visualization: Modern Approaches" which includes a ton of cool infographics like this one:
I played around with visualizations using Processing and I hope to get back to that sometime soon. It's a very fun and surprisingly interesting area.