Google-maps – send a postcode direct to Google Maps in the URL

You can share maps from your old account to your new account by using the Collaboration feature. I don't believe it's possible to share all of them at once; you'd have to do them individually.

Go to Google Maps, and click on "My places" on the left sidebar. Find the map you want to move over. Click on it, then click the "collaborate" link. From there, invite yourself as the collaborator, then send the invitation. You'll then be able to access the map from your new account.

According to The New Google Maps, Now Available (May 17, 2013)

"My Places" is not part of the new Google Maps interface. Click the "options" icon in the black navigation bar, select "My Places" and you'll go back to the old interface. It's a trick that lets you temporarily switch to the old interface. You can also click "classic maps".

However you can still access your "My Places" by going directly to Google Maps - My Places which will contain all of your old maps (which are still editable).

You can also use Google Maps Engine Lite to create and view custom Google Maps.