Canine Cancer (on Yahoo Groups)
http://groups.yahoo.com/group/CanineCancer/
With over 1,000 members, it's a fantastic place to find people with similar experiences and a wonderful place to find support through the difficult journey ahead.

Canine Cancer Support (on Yahoo Groups)
http://groups.yahoo.com/group/CanineCancerComfort/
With almost 200 members, one more place to look for information to compare treatment methods and exchange experiences and support from others.

Dog Health (on Yahoo Groups)
http://groups.yahoo.com/group/DogHealth/
With over 1500 members, a great place to look for nutrition information.   It is becoming more accepted among the veterinary community that diet may be the key to preventing some forms of cancer.  This is a great place to start.

Financial Support Organizations
IMOM - http://www.imom.org/
United Animal Nations - http://www.uan.org/lifeline/index.html
These organizations can help financially with escalating vet bills.
There are strict qualifications, and clearly thousands of requests to sort
through, but if you truly cannot afford the treatment your dog requires
this may be a valid option for you to pursue.