Here is a systems I worked of late but still really early days.
All testing is only from Jan 2008 - 2/7/11
Some have a few too many rules but the results were good.
All made good profits, but most punters expect to make money every weekend so could be of no interest

Saturday Only
a) Distance 1110 - 2000
b) Field size 14+
c) Age 3 +
d) Place 21%+
e) Weight max 58kg
f) Weight below top max 5.0kg
g) Days Last Start = 10 Days (important)

Last start must be metro and within 4.9 lengths

403 Bets - 54 Winners (13.4%) POT
696 Return , POT 72.7% Unitab

Enjoy