I haven't come across a promo code for a discounted or free Sirius satellite radio since before Christmas until tonight.  Someone posted in a stock newsgroup this code which invokes a $100 dollar discount.  The car kit is $50 and the home plus car kit is $100 with the discount.  The prices on the site change when the code is entered.

Promo code 113

https://home.sirius.com/webDUWI/HomePage.aspx