Once you've digested that you probably want to try practicing the first two units in our rhythm anthology.
Also you can try a worksheet on counting and check your work with an answer key.
Apps and Programs
In general it seems that apps designed for rhythmic practice are a little more difficult to design than the note-reading quizzers we've already seen. These are all a little crude and weird but they may be worth trying.
PC / Mac
Robert Whelan has a rhythm driller at emusictheory.com. As always this will work with any java-enabled browser.
iPhone / iPad
Rhythm Sight Reading Trainer ($3) is the best thing I've found. The interface takes a few minutes to get used to, though.