Best thing I have found for motivation is a goal - something you want to be able to do. Is there a metric century or century in your area you might train for? Are there any groups in your area you might ride with who have casual paced rides you could join and start to get motivation from riding with others?

You say you have a lot of hills in your area - do you have an altimeter or other way of measuring those hills so you can start to compare one ride to another? If you do a 30 mile ride that has 2500 feet of elevation gain, that should take you a lot longer than a 30 mile ride with 1000 feet of elevation gain. Unless the wind is blowing really hard. Which goes back to my original mention of "conditions".

You can also set goals of trying to improve your time on specific rides, etc. There's plenty of competition you can find with yourself.