Affiliate Marketing Networks:

http://blog.clickbooth.com/ – Clickbooth

Competitive Intelligence:

http://cubestat.com/ – Find out how much a website is worth, how much they are making with ads, not always accurate, but a decent estimate.

http://www.myipneighbors.com/ – Have a shared hosting account? See who else is on it.

Computer Programs:

7zip – My all in one zip program, its free and does everything.

Market Research:

http://www.alexa.com/

http://www.quantcast.com/

http://compete.com/

http://trends.google.com/trends?hl=en

http://www.statbrain.com/

Creating Advertisements:

http://www.livemercial.com/ – Create your own infomercial

Pay Per Click:

http://www.komarketingassociates.com/blog/200-plus-negative-keywords-to-consider-for-b2b-ppc/ – List of Negative Keywords

Social Networking:

http://www.meetup.com/ – Meet in smaller local groups

http://wildfireapp.com/ – Organize contests on Facebook, Ning, Twitter, etc…

Web Design:

http://browsersize.googlelabs.com/ – Curious on what internet surfers see?