I've been volunteering at an animal sanctuary (mostly horses) and that exercise has certainly made a difference to me in a short space of time.
I do have an exercise bike which I really need to start using
I think it does lift my mood (mostly) but I guess it's the improvement in appearance/fitness that raises my self esteem somewhat (shallow I suppose) that helps.
I'm terribly unmotivated though. Which is why the a. sanctuary has been great cause you kind of have to turn up whether you feel like exercise or not, lol.