Thanks everyone, appreciate all the responses.  I love the look and intensity of a Border Collie but have heard as you said they have to be kept really, really busy.  Here in suburbia we compensate that way with flyball:
http://www.flyball.org/nafa.html
Here are some flyball videos:
http://www.youtube.com/watch?v=X64NC0oQdPI
I often wished I had a dog I could train to do flyball.  It's so exciting to watch the dogs race back and forth, but I think it would be even more exciting to watch a dog work cattle!  I've watched different breeds of dogs do flyball, and it's always the border collies who go faster than a swift straightline wind, and with rabid focus. 

Maybe more a Kelpie or Blue Heeler or English Shepherd for us though--we've only got a few cattle.  I'm sure I could think of more things for the dog to do.  My dog now will go get anything if you point at it so he's pretty smart but he's an indoor dog and he's 10.  We need a rough-n-tough outdoor working farm dog in addition. 

For those who have English Shepherds--I looked at some pix on the internet but they all look so different--could you post pics of your English Shepherds please?