...plant to keep weeds down? I am clearing a lot of scrub and small trees from the wooded space behind my house. How do I best keep the weeds, scub from coming back? If I plant grass it will look like a prairie because I don't want to keep it cut like my yard. I don't know if wildflowers grow in the shade. I'd like to avoid the exprense of mulch. Any ideas?

I know something that will work well for you. Vinca. I have it in my yard and it is a bit too invasive for me, but a wooded area would be great. Vinca is a ground cover that likes shade. It grows around a foot tall and has pretty blue flowers when in bloom. It spreads quickly and can be trouble if it gets in you garden bed, however, it is shallow rooted and comes out easily. Here is an article about Vinca minor. You can find it in almost any garden store. http://hortwww-2.ag.ohio-state.edu/hcs/TMI/Plantlist/vi_minor.html

Some people use old carpets to supress the weeds. After a while they take them off. I don't know much about it though, maybe someone will explain you more about the carpet.
But I know where to get old carpet from - if you failed to find it in the scrap yard, you can look for it on www.graiglist.org in USA or, if in UK on www.freecycle.org