The Lib Dems say "Vote for us, we want to put sprinklers in the new Mayfield school." (innovative policy there, given the last school burnt down).
Labour say "vote for us, because there shouldn't have been a by-election in the first place. Or maybe there should have been one sooner." (innovative lack of policy there). Update Stop the presses - in the body text below the innuendo and mud-slinging I found policy, the Labour candidate wants better street lighting.
The Tories don't say much, IIRC the one leaflet I've seen from them (and have since recycled) said something like "Vote for us because we run the County Council already." I think there was a UKIP leaflet too, and I see Stephen Lawrence is running for the Greens as usual.
Odd that there's so little communication from everybody except LD and Labour, I guess that a December by-election in a fairly solid Lib Dem area isn't really worth much effort.