The Sirius website have a promo on the Sportster 5 (the full color receiver that is actually the only Sirius receiver to get good reviews) for 125$ with a three-month subscription (15$ activation + 13$/mo service).
If you apply coupon SIRIUS15, it comes down to 106.25 + tax (shipping included)
There may be a 10$ FW CashBack as well.
NOTE: This also seems to work if you currently have a subscription and want a second radio; if you are logged in when you start the deal (don't forget FW CashBack first), it will list 21$ for subscription and 15$ for activation.
I have a Sportster 3 and don't know how I lived without Satellite radio before. You can try the online trial with a junk account to see if you like the music lineup, or use Playlist search to search for favourite artists.
