If you have a backup, you can retrieve it from there.
If you don't then the process gets much, much harder, and you should consider implementing a backup system as a matter of priority.
Basically, if you don't have a backup, you are stuck with retrieving the data through the transaction log. There are companies that can help you -
http://www.apexsql.com/sql_tools_logapi.aspx[
^] have a free 14 day trial, which may be enough to get your data back.
And then BACKUP!