I overdid legs too on Sunday and there is NO WAY that I could work them again today! Heck, I can barely do stairs at this point!! I've never done legs more often than twice in one week - once heavy and once light. I'm debating doing Legs Lite tomorrow - low weights, high reps.
As for cardio, I do it just about every day but always make sure to do it early on Leg Day - I don't think I'd be able to do cardio afterwards. On the Day After Leg Day, I often do the bike because it stretches out my sore muscles and seems to help. Today (two days later) I did 20 minutes on the crosstrainer (which just about killed me) and 20 on the bike.
Aren't massages the best?