I use two test generators that work pretty well to import my own questions. I use Test Wizard, http://www.testwizard.com. I create the test in test wizard, then I save it as a PDF. I open the PDF in Adobe Acrobat Pro and save it as a Plain Text file. I open the plain text file and modify the format to match Aiken format, which moodle can read. That is faster than retyping or cutting and pasting individual questions. The images are lost in the TXT file conversion, so I have to go to the images in the PDF and take a snapshot, which I save as a JPG, and then edit the questions in moodle that need images by inserting the JPG. I know it seems like a lot of steps, but again, easier than typing them all in moodle manually.
The other test generator I use that comes with a lot of textbooks is ExamView. ExamView works a little more seamlessly in that from ExamView you can export the test to Blackboard format. Moodle can import the Blackboard format directly. Images still need to be imported.