Sources

I learned a lot from my student teaching, but one very important lesson I learned was that it is just as important to be knowledgeable as it is to be resourceful. You definitely need to know your content area, but nobody knows everything. As I was planning lessons, I found out that there are a lot of trivialities and minor details that I couldn't remember from my undergraduate program. Luckily we have the old www to fall back on.
The best site that I have found for pure math questions has to be Wolfram MathWorld. This site has everything you need to know and much more. Just type in a search query and a list of results pops up. You should be able to find out just about anything that you need.
Something else I found to be a real time saver was to have someone write my lesson plans for me. With Purplemath you can do exactly that. They have a catalog of lesson plans for Pre-Algebra, Algebra 1 and Algebra 2. I wouldn't recommend relying on this regularly since you'll probably have to tweek the lessons a little to fit them into your class but it can come in handy every now and then.
Another thing I found myself spending a lot of time doing was writing worksheets. Luckily there are plenty of good worksheet generators online. One pretty good one I found was EraserDog. This is a pay-optional site but you can get everything you need for free.
There are plenty of other sites that I frequented during my student teaching, but I thought this was a nice blend of things that are useful to new teachers.