I have Bridge (and also Bolt App), but I'm using those mainly to bring in ringtones/alerts.
I keep all my music in my iTunes library on my Mac, but I also have the Google Music Manager which uploads direct to Google Music (or Play, or whatever they are calling it now). I use an app called gMusic which allows me to directly access my entire iTunes library that's up there in Google Music and stream it to my device. The music controls for the iPhone work with gMusic so I can control it just like if I had actual music on my iPhone. There's even a music tweak on Cydia that allows me to control playback via my volume buttons which because gMusic works with the standard iPhone music controls means this tweak can control gMusic.
All of this to me is great because I get access to my entire iTunes library, but zero of it is stored on my iPhone - so none of it takes up any storage space.
Of course I need a WiFi or cellular connection to stream, but there is no shortage of either in the places I tend to be at.