How did you partition the drive? If you selected the device and then chose "2 partitions" or more from the drop-down menu in the Partition tab of Disk Utility, then you rewrote the partition tabels and lost the data.
On the other hand, if you selected the current partition scheme and clicked the plus button at the bottom to add a new partition to the existing partition tables, then you should not have lost data, though it is possible you ran into an error that did result in data loss.
You can try using a program like Disk Drill, Prosoft's Data Rescue, or the recovery tools offered by Stellar Phoenix as options to try; however, these can be hit-or-miss.
One option you can try is the Terminal tool TestDisk, which may help rebuilt the lost partition table, though it may not work since you have a healthy partition table and formatting, just not the one you want.
To do this, download TestDisk from here: http://www.cgsecurity.org/wiki/TestDisk_Download
Open the TestDisk package and it should unzip and give you a folder with some items in it. Now open the Terminal and type "cd" followed by a single space. Then drag this folder to the Terminal window and press Enter.
Once this is done, run the following command:
Supply your password when prompted (it will not show), and then use the arrow keys and on-screen instructions to select your external drive and attempt to repair it. There's no guarantee this will work, but its worth a shot before you give up on the drive.