There are some really good tests available - Anything that runs on "the mother of all booktests" principle is worth buying, as reverhart mentioned, these can be expensive, but the spectator handles the book at all times, can choose any substantial word they wish out of the ENTIRE book, they can be very strong indeed.
There are plenty of reviews on book tests around check out
www.themagiccafe.com for further info.
For something a little more interesting, try
www.outlaw-effects.com - I got their homicide book test about a year or so ago, they have some REALLY cool and unique products.
D.