What would be a good ground cover (or any other type of plant for that matter) that I can use in the bare space left after my spring flowers bulbs are gone? I don't want anything with roots that would crowd out the bulbs.

You can use just about any cool season ornamental, such as pansy, viola, Iceland poppy, etc. You'll need to space them out a little farther than you would normally, when you're overplanting bulbs. Plant 4" pots on a 12" center. That will allow enough room for the bulbs to maneuver around the roots while emerging. If you're planting tulips, daffodils, or any other large bulbs, make sure to plant them a good 6" deep in the soil.