Ask HN: What are some cool and useful hacker sites?

Some sites – like HackerNews – just make life easier/better. Here’s a list of ones I’ve found over the last year.

Do you know of any sites that should be on this list?

Cool/useful sites:

TED – life changing talks

Fiverr – random stuff just $5

Quora - Q&A made cool and fun

StackOverflow – Q&A for coding

Flippa – buy and sell websites