I've always heard post weight lifting is best for cardio and fat burning but I just can't do it. I'm reduced to jello post lifting and cardio isn't do-able. So I usually do spinning, x-trainer, uphill walking first.
Anyways, I do 15min HIIT twice a week, non leg days of course. And I'll do 20-25min of med intensity cardio two other days. Otherwise I'll do a 5 min warm up other days.