I love the one that came with my Singers XL5000&6000:
http://cart.jennys-sewing-studio.com...oducts_id=1553


That looks OK, but it's flat, so I still would have to use my other hand to
change my grip every 180deg.

But your question encouraged me to do a search. I may invest in one of
these:
http://www.cmlsupply.com/right-angle...Fe-DQgod7W0AXw


Pretty good price too.