The writing of textbooks and making them freely available on the web is an idea whose time has arrived. Most college mathematics textbooks attempt to be all things to all people and, as a result, are much too big and expensive. This perhaps made some sense when these books were rather expensive to produce and distribute--but this time has passed.
George Cain has done a great job in compiling all the free mathematical text books that can be accessed online as well as downloaded online. Some of them are in HTML and others are inPDF formats. He says it is not comprehensive but he is adding it every day and many have told him that they are an excellent source, so he is maintaining that site for a long time.
Too bad, it wasn't available when I was taking Math classes. If you are in Math or in research you will find this link useful.
Here are a few textbooks available:
* Multivariable Calculus by Jim Herod and George Cain
* Calculus by Gilbert Strang
* Linear Methods of Applied Mathematics by Evans Harrell and James Herod.
* Linear Algebra Infinite Dimensions, and Maple by James Herod.
* Partial Differential Equations by Professor Herod
* Complex Analysis by George Cain
If you research more online, you will find free books for other fields, a good place to start is Google Book Search
and Google Directory