I ordered "The Heart Rate Monitor Workbook for Indoor Cyclists" by Sally Edwards last week and it finally showed up yesterday. I've been flipping through it this morning and it has a ton of indoor workouts that all revolve around heartrate monitoring but I think it is going to be pretty useful to keep the rides interesting actually. They seem pretty detailed in their structure so I think it will break up the monotony pretty well... i hope.
http://www.amazon.com/exec/obidos/tg...books&n=507846