Need help with my Running Form

Although I've been running consistently for about 6+ years now, I never really worried about my form as I do with swimming and biking. I want to continue doing marathons (i've done 3), but I think more than anything, my limiting factor is form. I've followed HR training; I've tried different plans - some with speed work, some without. And I've seen what helps and what doesn't, but I just don't seem to be getting as much out of it as I've put in. Which all leads me to think that I'm just not as efficient of a runner as I should be.

Anyone know of good resources to read/watch to learn more about proper form? Websites, books, anything else. How about drills - what are some good ones to do, and how often?

I was considering getting the Triathlete's Guide to Run Training. Ken Mierke is a BT forumite, right? Does this have what I'm looking for?

Thanks for the help.

Walt