Below are the most useful tools I have found for my math assignments. They are mostly calculators, but I may also include graphing tools and other useful stuff.
SpeQ Mathematics all-in-one calculator
SpeQ is pretty awesome. However, it looks terrible by today's standards. It is easier to use than any other calculator I know of. Of course, it caters to programmers and like-minded people who like to type.
SpeedCrunch all-in-one calculator
Most people find this one easier to look at than SpeQ, but I ultimately prefer SpeQ for how fast and efficient it is. Both have their pros and cons, so I use both.
More tools later!