One of the leading organizations for this cause, and a great resource for all things pollinator related is pollinator.org. Their mission is to protect pollinators, critical to food and ecosystems, through conservation, education, and research. Signature initiatives include the NAPPC (North American Pollinator Protection Campaign), National Pollinator Week, and the regional Planting Guides. Be sure to check out the regional planting guides on their website. Once there, input your zip code and it will give you an informational guide (.pdf) for selecting plants in your area for pollinators along with other useful information about the pollinators in your area. Here is the regional guide for my area: http://www.pollinator.org/OuterCoastal.rx5.pdf
In addition to planting a variety of pollinator favorites, you can also provide housing for our native pollinators like the orchard mason bee and the leafcutter bee. Here's a photo of my mason bee house.
Mason bees nests in natural holes, creating individual cells for their brood that are separated by mud dividers. Unlike carpenter bees, they cannot drill there own holes in wood. They will often use holes created by carpenter bees or any other small hole or crevice found in nature. They are great pollinators to have around for your garden, and you can help attract them by purchasing or making one of these houses for them.
I put my house up a little late this spring so I haven't had any mason bees in it but it has attracted a few leafcutter bees. Like Mason Bees and just as fascinating, leafcutters have a similar nesting style and will nest in the same wooden bee houses except, as their name suggests, they line their cells with small pieces of leaves instead of mud. Here's a close-up comparison:
Mud sealing - a Mason Bee hole
leaf sealing - a leafcutter Bee hole
Leaf cutter bees are also great pollinators to have around.
Check out these links for more information on our native bees, as well as attracting and constructing housing for them:
Information about solitary bees and attracting them: http://wingsinflight.com/gardbees.htmlManaging and instructions on building a mason bee house: http://www.ces.ncsu.edu/depts/ent/notes/Other/note109/note109.html
Great site about native bee conservation: http://www.ournativebees.com/home.html
Also, check out the pollinator page over at the U.S. Fish and Wildlife Service: