I am trying out Xbian on my Pi http://xbian.org/
and it works really well, although it is difficult to keep up with as the dev seems to be releasing updates every other day or so, most updates can be applied without the need of re-imaging the SD card.
My latest accessories for my are a Edimax WiFi dongle http://tinyurl.com/czbbsk5
or there is this one http://tinyurl.com/buhqxh4
that is a bit cheaper, a mini wireless keyboard/touchpad http://tinyurl.com/9apdy78
which is fantastic and a decent power supply http://tinyurl.com/8m3v5aq
which has no problems powering WiFi and the keyboard.
XBMC-XBian, so far seems to be really good solution for streaming media form my media server, and I am sure XBMC-XBian will only get better through time. I can stream avi's over WiFi, I havent got a fast enough wireless network for HD content, from what I can gather wireless can give issues for HD streaming, I can also control XBMC from the app on my Android phone.
I also have other SD cards with different OS's installed including a 16GB card with Raspbian installed, the official distro of the Raspberry Pi foundation, an 8GB card that dual boots with RaspbRazor http://tinyurl.com/dyyt8to
and OpenElec another XBMC port.
Ian, if you havent got a slice of Pi, then it is high time you did, if nothing else they are a great toy.