If we're strictly discussing test practice for verbal, then there's not too much out there beyond the obvious resources. You already mentioned the six MGMAT online tests. I don't have any experience with the Knewton CAT's, but people seem to like them. And, of course, anything from GMAC is reliable.
If we expand our search to include questions as well, then we have the many problems posted on GMATClub and LSAT question banks for RC and LR. Also, look into the Brutal SC document
To be honest, everything mentioned in this particular thread should be more than enough. Just make sure to completely read the explanations - even for the questions that you answer correctly.
GMAT Club Premium Membership - big benefits and savings