One problem with companion plant groundcovers with bulbs is the companions
will often need watering through summer when some if not most bulbs are
dormant & regular watering would cause them to rot.

I've found ornamental strawberries can get by without TOO much summer
watering, plus can bloom spring through autumn.
http://www.paghat.com/strawberrylipstick.html

Campnula poscharskyana, or Serbian bellflower, also thrives with spring
moisture & summer droughtiness, & in my zone blooms for about six months
right into the heart of autumn.
http://www.paghat.com/campanula10.html

Dwarf lemon thyme is a good groundcover companion for the sorts of tulips
that need it very dry in summer.

Ballotta nigra 'Variegata' is a loosely trailing groundcover; the root
remains a clump but the branchings can cover a four by four foot area, & I
have it planted with two-foot or taller tulips.
http://www.paghat.com/horehoundvar.html

Several other herbs do well in lots of sun without need of too much
watering & remain short enough & not too densely rooted that they do well
well over bulbs. Such as Tricolor marjorum:
http://www.paghat.com/marjoram.html

-paghat the ratgirl

--
"Of what are you afraid, my child?" inquired the kindly teacher.
"Oh, sir! The flowers, they are wild," replied the timid creature.
-from Peter Newell's "Wild Flowers"
Visit the Garden of Paghat the Ratgirl: http://www.paghat.com