OOh, i will be watching to see what the gardners say. I'm fairly rookie, so take MY word with a grain of salt, but i THOUGHT that most ground covers DID allow spring bulbs to pop up through them? ...common ground covers, like vinca and pachysandra(which is a lil taller for super-short bulbs to get through though..)
Now, 'white nancy' nettle i can personally attest to the fact it WILL allow bulbs up through.

Pachysandra may not allow bulbs through when it's fully established - it's a pretty compact network of underground runners, fairly shallow, but I would doubt that bulbs would pop through long term. I planted this to get rid of Bishops Weed in my yard. It eventually choked it out. I thought of trying this at one point, with the bulbs, but decided against it based on more research.

I would think Vinca would be fine, and I also agree with Lamium.

Ajuga???? Not sure, really, but I'd like to know.

Lady's Mantle will grow in part shade, but not full shade. Let it go to seed and it will self sow. This may be another option.

http://www.ehow.com/video_4753996_grow-ladys-mantle-alchemilla.html

Pulmonaria aka Lungwort? more clumping habit, but great flowers in shady areas

Pulmonaria lets spring bulbs through, not problem and it is beautiful with them, too. Needs lots of moisture to get full. I have a lot of it, but it has only gotten lush and full where my sump pump drains!