Besides gaining reputation with your questions and answers, you receive badges for being especially helpful. Badges appear on your profile page, flair, and your posts.

Question Badges

Ask a well-received question on 30 separate days, and maintain a positive question record
2 awarded
Question saved by 25 users
Question score of 25 or more
2 awarded
Question with 2,500 views
1 awarded

Answer Badges

First to answer and accepted with score of 10 or more
5 awarded
Edit and answer 50 questions (both actions within 12 hours, answer score > 0)
Answer saved by 25 users
Provide non-wiki answers of 15 total score in 20 of top 40 tags
Accepted answer and score of 40 or more
Answer score of 5 or more to a question score of -2 or less that goes on to receive a score of 2 or more
Answer score of 25 or more
1 awarded
Answer a question more than 60 days later with score of 5 or more
6 awarded
Zero score accepted answers: more than 5 and 20% of total

Participation Badges

Vote for a candidate in the final phase of an election
Leave 10 comments with score of 5 or more
Visit the site each day for 30 consecutive days. (Days are counted in UTC.)
24 awarded
Earn 200 daily reputation 50 times
Voted 10 times, added 3 posts score > 0, and visited the site on 3 separate days during the private beta
Post 10 messages in chat starred by 10 different users
Active member for a year, earning at least 200 reputation
1.3k awarded

Tag Badges

You must have a total score of 400 in at least 80 non-community wiki answers to achieve this badge.

Moderation Badges

Raise 80 helpful flags
Vote 300 or more times
3 awarded
Complete at least 250 review tasks. This badge is awarded once per review type
Edit 80 posts
Edit 100 posts that were inactive for 6 months
Up vote 100 answers on questions where an answer of yours has a positive score
Edit 50 tag wikis
Create a tag used by 50 questions

Other Badges

Share a link to a post later visited by 300 unique IP addresses

Retired Badges

Completed the annual Stack Overflow survey; your responses are anonymous