drop box works well and its free (tho free version limits capacity, you can add more by referrals, installing app, etc...)... you can increase storage by paying $ too.
On phone it shows only the list of files (with thumbnails for pics) which minimizes data overhead...but downloads file if you tap on it...syncs with PC, mac, and iPhone too.
You might be able to set sync setting on phone app to only do over wifi...I do know you can have it cloud/sync pics over Wi-Fi only...
Edit - you can toggle phone sync for drop box account on/off but only picture sync can be set for Wi-Fi only...
There is also 4shared...basic service (of course with limited storage space) is free