Game consoles like the Xbox 360 and PS3 use UPnP/DLNA to access media from other devices like computers that are on the same network. You can share media from your Android device to XBMC or any computer that can connect to Windows file shares with a Samba server app like the one I've been using, but to share videos, music and photos with an Xbox 360 or PS3 you'll need a UPnP/DLNA server app like iMediaShare. It's a free download on the Android Market.
I stumbled onto iMediaShare a while ago and used it to display photos taken during the holidays with my Android phone, an HTC Inspire 4G running CyanogenMod 7, on a TV that was hooked up to an Xbox 360. It's a quick and wireless way of displaying photos for a group of people to see on a large screen and certainly beats having to pass around my phone so everyone can see the group picture I've just taken.
Note that the Xbox 360 (and likely the PS3, I've never used one) can't playback every kind of video format that you might come across. Even with all the codec updates that have come out for it I think an original Xbox running XBMC is better for playing back all non-HD video formats. So don't expect every video you try to share with your Xbox 360 using iMediaShare to play correctly.
Music streaming of MP3 and AAC audio should work well with the 360, but I haven't tested this out myself since I don't have a 360 to test with at home.
iMediaShare also has an iOS version in the iTunes Store. I'm keeping it installed on my phone, it's a nice addition to my collection of Android media apps which includes things like Moboplayer, XSpeedPlayer and the remotes for XBMC and the Roku box.