What type of weight training are you doing? Over the last few years, I've become a huge fan of high intensity circuit training using lower weighted dumbbells or body weight exercises. It's basically mixing weight training and cardio into the same workout. The name is hokey, but I've taken a workout I saw in Men's Health called "The Spartacus Workout" (http://www.menshealth.com/mhlists/hi...tine/index.php
) and created a bunch of variations to keep it fresh.
What I have found is that my "practical strength" is much better going into the spring over the last three winters of doing this. This has led to me being much better prepared for my two favorite sports, tennis and mountain biking, right away in the spring. I've also found my aerobic levels to be better than past years when I've separated my weight training from my aerobic workouts.
I know you asked specifically for a cardio routine and my response wasn't deviated from that a bit, but thought I'd mention what I've found effective. If it's not for you, maybe somebody else might latch on to the idea.