There's the standard list of scholarship search sites like FastWeb, Cappex, Sallie Mae Scholarship search, etc. There are also manually updated lists of scholarships like the Best List of College Scholarships
or the lists posted on guidance department websites. Any scholarship you get from these sources should be legit, especially the manually edited lists since someone is actually reviewing and researching the scholarship before adding it to the list.
One piece of advice that could be helpful:
Don't limit yourself to your guidance department's scholarships. In other words, visit the web sites of other local high schools' guidance departments and look at the list of their scholarships. Some of these will be specific to their school, but you may find some scholarships you're eligible for that you didn't know about before.
Hope this helps!