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 Bone Cancer (on Yahoo Groups)
http://groups.yahoo.com/group/CanineBoneCancer/
Another fantastic list with over 350 members and dedicated specifically to Osteosarcoma or bone cancer.  Another great place for information.

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.

Endless Love (on Yahoo Groups)
http://groups.yahoo.com/group/endlesslove/
446 members for people with pets with Cancer, yet another highly active list to look to for support and information - and sharing your experiences with 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
Help a Pet - http://www.help-a-pet.org/home.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.