I use Reason
http://www.propellerheads.se/
It is for windows. It is a great product you do however have to purchase it. It is rather expensive as well. They have a great forum, wich you must register for, and register your product to reach some boards.
It also does have a learning curve, but you can sample loops, create, your own music, it has several virtual production equipment.
Check out the site it is great.