I agree with the above comments about changing routes or fiding some other activity for a while. Just make sure it's an active hobby like hiking or swimming.

Also, it helps to set some sort of achievable goal to work toward. Not neccessarily a mileage goal. Rather, try to find some event that you would really like to ride that requires training. For me, I wanted to ride the OK Freewheel all the way across Oklahoma. It was important for me to ride the entire route and not walk any hills. This provided motivation for about 9 months to ride frequently and even put up with an indoor trainer during the colder winter months.

Even smaller goals can be useful. Working toward riding a century (english or metric) at a specific upcoming event can provide motivation.

Sometimes when I get home I feel tired and start looking for excuses not to ride. I remind myself that I should be looking for excuses TO ride. Hook up the trailer and go grocery shopping. Bike to work, if possible. Vow not to drive your car except to and from work. Promise to do some kind of riding every day - even if just around the block. I find that just getting on the bike revs me up and before I know it, I've ridden 20 miles.