When you don't really have anything to train for, it's hard to stay motivated and not get bored with the training. However, it is also a good time to relax somewhat from intense training and give your body a bit of a break. I looked on runnersworld.com to see if I could find a good maintenance running plan, but there was none to be found.
So, I made up my own...
Mon: 1.5 miles warm up, 3 miles intervals (e.g. 2 x 800m; 4 x 400m with recovery periods in between), 1.5 miles cool down
Tue: 20 min elliptical + weight circuit x 3 (I use the ABS Diet program for strength training)
Wed: 5 miles easy
Thu: 20 min elliptical + weight circuit x 3
Fri: 6 miles with 1-3 miles tempo or 6-9 min hill running
Sat: 30 min elliptical (or easy run) + weight circuit x 3
The experts also recommend you sign up for a spring race so you have something to look forward to. active.com is a good site for finding races in your area by type, distance, and several other criteria.
Just keep running.