Product & Design
Jackie Bavaro's "The Art of Product Management" blog: http://pmblog.quora.com/
Ben Horowitz's classic "Good Product Manager/Bad Product Manager": http://a16z.com/2012/06/15/good-product-managerbad-product-manager/
Pttrns.com - the best resource I've found to reference design patterns: http://pttrns.com/
Find, Vet, and Close the Best Product Managers: http://firstround.com/review/find-vet-and-close-the-best-product-managers-heres-how/
What Does a Product Manager Do? : https://medium.com/@tworetzky/what-does-a-product-manager-do-205b40d82da3#.yqo96lf6z
UX Checklist: http://uxchecklist.github.io/
General Cool Tech Stuff
Animated Tabs - a fun Chrome extension that shows you a gif or a serene "work mode" image any time you open a new tab: http://animatedtabs.com/
Trello - the easiest way to manage a project: https://trello.com/
Commit Logs From Last Night (pure entertainment value when you need a laugh): http://www.commitlogsfromlastnight.com/