My company, instaGrok, is an interactive research engine for school students. Our interactive interface makes research more actionable and engaging than traditional search engines.
Give it a try and let us know what you think! We're always looking for feedback from new users.
Can you be more specific about the subjects?
Some quick suggestions: for medical and free (www.pubmed.com which contains everything in the National Library of Medicine) or physical sciences (the Web of Science allows you to find both very very old things and the newest articles/conferences etc--but it is expensive--usually only can get access at universities).
I use www.dogpile.com to find things on the web because it is a meta-search engine meaning it gives you the results from several popular websites.
Next time you are in any library, chat with the reference librarian (smiling...I'm one) and ask her/him for their suggestions.
Good luck, searching!