Here's another resource. If the MOEMS problems become too easy (or if you just need to return the book to the library :-) try the AMC8 tests. 25 multiple choice questions that start pretty easy and get progressively harder. I forget what the time limit is. It might be 40 minutes. The 8 in AMC8 indicates that these questions are for 8th grade and under.

Lots of tests and solutions here: http://mathjunk.googlepages.com/amc8