Lily of the valley has a pretty invasive root system. You may have to thin it every year to plant anything among it. Annuals you could try would be impatiens, or coleus. They grow well in full shade, stay short, and would add color. If you want perenniels, you could plant painted ferns between the shrubs and the lily of the valley. They would also add some color texture, and height to the middle of the bed.
Colleen

How about astilbe for some height and color? They are right about having the thin the lily of the valley the roots get pretty thick and may choke other things out. I think ferns would be strong enought to come though though.
Catrina

Bleeding hearts. I have three in nearly full shade, and they bloom and last until late July.
Astilbes are lovely too, as Catrina said, but need alot of moisture. Daffodil bulbs would give wonderful spring punch. pansies and ferns look interesting into the summer.
I've had some sedums do very well in shade too. And, of course, quite a few annuals will give summer color, like begonias and impatients and caladium and coleus, as mentioned above.
Pondy

If you're gonna thin out those lily of the valleys and need someone to take them off your hands, I'll come get them...just a thought...! :-)

I've got forget me nots, balloon flower and sedums doing great in the shade at my place, along with the bleeding hearts and astilbes someone mentioned. The Forget Me Nots and balloonflowers reseed like crazy so I think they'd probably handle the lily of the valley's crowding ok.
Karen

These are all great suggestions. Thank you. Could someone let me know how and when to "thin" the LOV? They are just starting to poke through now.
Melissa

I usually thin mine in late summer, early fall when the foliage dies back. You might lose some of the blooms by doing it in the spring. As for how, I'm brutal. I just rip them out and give them away. I don't you can kill them. I forgot about some bare roots after thinning once and they were putting out shoots next spring, in a cardboard box with no soil, in the garage! I planted them and they grew just fine. Good Luck!
Karen

My mother has a huge L.O.V. patch in a very shady location (under a chestnut tree). As a child, I planted some Jack-in-the-pulpits & L.O.V. there, among other things which mostly failed. Those two, however, co-colonized the entire area. The moist ground beneath the L.O.V. canopy acts as a perfect incubator for the J.I.P. seeds. The deep green leaves grow to about a foot high, and the bright orange seed clusters are attractive in late summer.

I haven't tried this combo myself but saw it suggested in a book ... lily of the valley with ajuga.

If you go with astilbes, the chinensis take drier conditions than most. "Visions" are gorgeous, and "Pumila" (sp?)blooms for months.

I have never been sorry for planting LOV, and have done so at several homes. Yes, they can take over a bed, but are easier than most invasives to control. I forgot to mention that when I replied to your post earlier.
Today, I smoothed some lotion into my hands and was just overwhelmed with the wonder of the smell of lov. umm, umm.
Pondy