I second airplayit. Great app and best of all, free
I recently came across AirPlayIt too and it works well and its free. It looks like a bit of an AirVideo clone but it does more than video, so...I currently use it for audio over 3G as Streamtome only works well from my home network for some reason, over 3G it times out a lot when listing directories, does anyone else have that problem? Doubt it's my setup since I have no such problem with Air Video or Airplayit.
A downside of AiPlayIt I've found compared to AirVideo is that it maxes out my Quadcore when streaming video, AirVideo does have peaks at 100% but goes up and down.
Will try Audio Galaxy that's been mentioned here as it seems to support more formats (no FLAC for AirPlayIt).
What would be great is an app with a browser or PC client to stream music or videos when you're on the go and don't/can't whip out the iOS device. Zumocast does that to some extent but I found it to be rather clunky.
edit : clearly AudioGalaxy does that, nice, unfortunately it doesn't allow you to browse through the folders of your hard drive, too bad, that's the way I like to do it...
I came across another app called Remote Potato but it won't let you choose the music directories you want to stream, so...
Plex is nice but like Orb it insists on indexing your whole library and I've found issues with that, mainly in terms of refreshing and making the host work hard in the background. When I checked it was the only app with an Android client though, there must be others now.
Oh and why can't StreamToMe or others that allow folder browsing offer "bookmarks", that would be nice rather than having to sift through folders...guess the answer to that is indexing like AudioGalaxy does.