I used Veritas - have to buy their tests but they're pretty decent. The veritas package also included 800score, arco tests.
800score is waaay too easy on the verbal and waay too difficult on the quant - that being said, I think the challenging quant helped me with my pacing/timing quite a bit; I just didn't use it as a predictor of the actual test.
The Arco was mediocre - quant was a bit more difficult than the actual test, verbal easier than the actual. The questions in both sections were of subpar quality. If it hadn't come with the veritas package, I wouldn't have spent $$ on it.
Have you tapped into the
MGMAT challenge question banks? those were great for quant!
hope this helps!
ac.