I use the FM transmitter available from the C. Crane catalog. Got it on sale for $50 (normally $70). I am very happy with it after years of frustrating drop-outs using the Sportster.
I did a manual adjustment on the unit using instructions from a thread in the old SBS forum to get it to broadcast perfectly all over my house without static. After the adjustment I found I have to put the volume on the transmitter very low although it plays at full volume on the radio. However, it is definitely better for talk as opposed to music. While music channels are listenable it takes a lot of tinkering of the volume on the transmitter to get the best sound.
I've had an old Pyle PLMD1 transmitter for about 6 years now. I paid 20 bucks for it.
Out here in the country it gives me a solid 1/4 mile range. My yard takes up 2 acres. When I'm working around the house, I put on a set of headphones and plug them into my little Sony Walkman.. I can hear my computer audio or the audio-out from my Sirius home dock loud and clear everywhere on my property. I have a set of noise canceling headphones that let me use the Walkman when I'm on my lawn tractor.
I don't know if you can still get the PLMD1 anymore, but there are a few sites on the net that advertise them:
Have a look on eBay. You might be able to pick up some Sonos gear there. You can also use an iPod touch or your computer as a controller, as opposed to using the Sonos hardware. I'm a huge Sonos fan and highly recommend it if you want a multi-room system. For a single room, there are cheaper alternatives.