Here are some of my top early bloomers.
Roughly in order of blooming

Golden Ragwort
Wild Sweet William
ZiZia aptera
Viburnum
Dames rocket
Philadelphia Fleabane
Dianthus - misc
Dianthus barbatus

Here is a link that might be useful: Butterfly Gardening

Sometimes it can be difficult to find early spring blooming plants, so I completely understand. That was something I worked on acquiring this year, but it will be next year before they actually do much.

Spring shrubs do most of the early blooming and Butterflyman mentioned viburnum, which is a good one, but make sure you get one that does bloom early cause I think there are some that bloom later.

Here's some more:

Spring beauty
Alliums
Snapdragons (don't know that they are very good nectar plants)
New Jersey Tea (ceanothus americanus) shrub
Gaillardia pulchella
Glandularia Canadensis or Rose Vervain
Native violets
Dandelions (these grow everywhere naturally in my yard, but the butterflies love em)
Clover (white)
Hyacinths (bulb)

Susan