Google Scholar - https://scholar.google.com/
If you're looking for a simple way to search forums and boards,
Boardreader serves up information contained in web forums and message boards. Multiple message boards can be searched simultaneously, allowing users to share information.
If you need to analyze what content performs best for a topic or competitor,
Enter your keyword and go! This identifies the most shared links on social networks, as well as influencers for specific topics.
If you're looking for media in the public domain,
creative commons is a search aggregator offering access to search results provided by a number of independent organizations. Don't assume the results displayed are under a creative commons license – always verify it, as sponsored results are served up, as well.
CrunchBase offers an unparalleled dataset of startup activity. More than 500,000 profiles of people and companies are maintained there by thousands of contributors.
If you're concerned about search privacy,
If you need real-time search for user-generated media,
Technorati uses tags that authors have included on their websites. These tags categorize search results, with the most recent results appearing at the top.
If you need access to the world's facts and data,
A computational knowledge engine that answers factual queries by computing the answer from externally sourced "curated data."
Yahoo bought Altavista and uses it as its search software