The best €2.50 I ever spent in the Netherlands was on a book of bike routes around Nijmegen, Fietsen vanuit Nijmegen (I got it on sale, otherwise the price would have been €9.50). There's a whole series of Fietsen vanuit... books, although if you live in Utrecht or Rotterdam, you're out of luck. The smaller cities, including Den Bosch and Zwolle and Deventer, are well-represented in the series. The books are printed by ReCreatief Fietsen, and these days, if books are too retro for you (they are, admittedly, a pain in the butt to carry while riding), you can buy map programs for your GPS from their website.
Each route begins with a map, depicting the route in red, population centers in brown, and most importantly, forests in dark green--this last is important if you're anything like Karel, and burn after 30 minutes in the full sun. Many of the routes in and around the Ooijpolder, for instance, are completely devoid of tree cover, so not doing one of those on a day of bright sunshine is probably a wise idea. That being said, even the routes that do offer ample tree coverage have long patches of farmland biking in between, so it's still a good idea to be liberal with the sunblock. Cafes, windmills, and castles you might see are all marked on the map as well.
There are also detailed directions on how to get from point A to...er, well, since these are closed loops, point A again. They also provide you with a distance-traveled-until-you-get-to-the-next-direction indicator, which is helpful but not exactly easy to use, since the numbers are cumulative--i.e., if something says 25.2 and the next one says 27.4, then you'd have stayed on the path for 2.2 km. I wouldn't call it difficult math, but it does take an extra step, and when you're thinking "We should be close to the turnoff point by now" and are looking for the telltale cafe, it's not exactly comforting to realize that you forgot to subtract one from the tens' place 20 minutes too late.
But the routes are well-thought-out, and are indeed well-suited for recreational riders. You don't have to be in anything resembling an athlete to complete a circuit, and the routes follow either well-marked bike lanes or less-travelled country roads which would meet even the most paranoid of Asian mothers' expectations for safety. Last Wednesday, on my last long bike ride until next year (it's getting risky now that the Little It is screwing with my center of gravity), we took one of the hilliest routes, but there was only one point where we had to get off and push our bikes up the hill, and that was a hill that I probably would have had to walk up even had I not been pregnant--it was that steep, although it was also a short one.
I've greatly enjoyed the rides this book has taken me on. They're not quite as easy to follow as the knooppunten, but they are lovely and very scenic and you don't run the risk of being faced with a downhill slalom or a cliff, nor do you chance being completely lost, or getting stuck on a road for three hours without a cafe in sight.