I found many of these links to be helpful when I was studying undergraduate mathematics

• Wikipedia
  Looking up math terms on Wikipedia can be hit or miss. Sometimes you get a very technical definition that doesn’t help much. Other times, you can get a definition in plain english with examples and maybe even a few mnemonics that aren’t in the textbook.
• Ask a Mathematician
  If you’re stumped on a problem, you can try posting it here and someone can help you if they’re able. Of course, it may take a day or two to get a reply.
• Sparknotes
  Sparknotes has an Algebra Forum and a Calculus Forum.
• Ask Dr. Math
  Another place you can post questions. Or you can search the archives to see if a similar question has already been asked and answered.
• Calc 101
  This online calculator can solve many derivatives, integrals. It can also perform long division and matrix operations quickly.
• Common Errors in Mathematics
  This isn’t really going to help you if you are stuck on a problem. But it might give you an idea where you’ve made your mistakes. If you’ve got a bit of time, you should read this article. It gives a pretty complete list of all the silly mistakes university students make.
• Karl’s Calculus Page
  Here’s a nearly complete page with a lot of calculus concepts explained in plain english.
• Mathworld
  This is an encyclopedia of all things related to math. If Wikipedia proves to be unhelpful, you might try looking here. On the downside, some of the articles can get pretty technical.
• Online Row Reduction Calculator
  Type in a matrix and this site will show you step by step how to row reduce it. (Note: There’s more than one way to row reduce a matrix, but no matter which steps you follow, you’ll always end up with the same row reduced form. So, it’s ok if you follow a different set of steps as long as the final row reduced form is the same).
• Paul’s Calculus Notes
  A detailed set of notes for first year calculus. Covers each topic and explains it in detail. Lots of examples and diagrams.
• Paul’s Linear Algebra Notes
  Same deal as above - just with linear algebra instead of calculus.
• Purple Math
  If you need to brush up on some high school math, this is a great place to do that.
• S.O.S. Math
  Similar to Purple Math, with more advanced topics. Also, the site has a great forum for looking for help.
• Calculus.org
  Lots and lots and lots and lots of links about calculus.
• The Integrator
  Type in your integral and this site will solve it.
• Math Joke Collection
  If you haven’t done much advanced math, a lot of these won’t be that funny. Even if you’ve done advanced math, many of the jokes are still not that funny.
• Graph
  This program is a very useful graphing program. Type in any function and it’ll graph it for you. A lot of other handy features. It’s easy enough to use that I can manage it.
• Microsoft Power Calculator
  Scroll down, it’s about the tenth thing listed on the page. If you don’t like using “Graph” (above), then you can try the graphing calculator from Microsoft.
• Math Tutoring
  This guy is an amazing math tutor.

If you use IRC, you can join #math on Efnet or Undernet and you might find some people willing to help you.