Restoring Orphaned MDF File in SQL Server

You can attach the database using CREATE DATABASE FOR ATTACH_REBUILD_LOG.

http://msdn.microsoft.com/en-us/library/ms176061.aspx

If that doesn't work, you can try the undocumented FOR ATTACH_FORCE_REBUILD_LOG.

CREATE DATABASE < YOURDBNAME > ON (FILENAME = 'D:\<YOURMDFNAME>.mdf')
FOR ATTACH_FORCE_REBUILD_LOG

From Management Studio

Attaching the .mdf file through the management console, without a .ldf file

1. right click "Databases" and select attach.
2. Click on "add" and select the .mdf file, click OK.
3. In the details panel select the .dlf file, click remove button.
4. Click the main OK button.