I found these sites very helpful when (hence the word *when*) I studied.  So I am passing on the wealth to you my dear friends.

pinkmonkey.com- this site has almost everything.   Help for most classes, book notes, tests preps etc...
http://www.studyspanish.com/tutorial.htm -for all you wanna be Spanish speakers, this is a muy bien help.
http://www.bbc.co.uk/education/languages/french/talk/index.shtml - french.  no comment
http://occawlonline.pearsoned.com/bookbind/pubbooks/campbell_awl/- The new AP bio book site.
http://dictionary.msn.com/- If you have a crazy English teacher like me, an online dictionary will really help.

*Also RHS provides a math study help called PAS-ME after school.   Monday's Mrs. D is in and Tuesday it's True, Wednesday I think its Mills and I'm not sure about Thursday, probably Thrasher, but I'm not sure he's holding up without Chester the math chicken.  There is no one there on Friday but if you are doing homework on a Friday afternoon you need more help than PAS-ME can give you...It's available from after school until 8:30.  Buenos Suerte!!