One of the resources I've found to be very helpful in understanding about my RA has been the online dictionary wikipedia, which is also full of a lot of other useful information.
Some of it can be heavy going, but I've always found it to be a pretty reliable source of information, and the folks at wikipedia are good about highlighting the difference between solid fact, speculation and unsupported opinions.
You can find them here at en.wikipedia.org.
Their entry for Rheumatoid Arthritis is here : en.wikipedia.org/wiki/Rheum...