bob's red mill
http://www.bobsredmill.com/not all of their products are from the USA, but a majority are. i emailed about beans and they sent me a very nice complete email back about where all their beans were from generally along with a few other things. and they were prompt! i use their products and if i have a question about where they're from, i just email.
Lundberg Rice out of California. Yummy!
http://www.lundberg.com/fresh/frozen clams (northeast)
http://www.nyseafood.org/members/doxsee/default.htmlgrass fed products:
http://www.eatwild.com/csa/farmers markets/ranchers/etc
http://www.localharvest.org/no matter where you live, if you think you may want to join a CSA, look NOW! they are already taking sign-ups here (brooklyn, ny) for the 2 i'm with for spring. i'm doing my deposits tomorrow. i missed out on one last season

and with the interest in better food growing with the general public, don't miss your opportunity!
these are my pics from the last half of the season. i started just taking one to send to mom because it was such a pretty assortment. i got a tad carried away!
http://www.flickr.com/photos/straybaby/collections/CSA's ROCK! check around for references in your area or at local farmers markets/organic sellers.
oops! forgot this one!
king arthur flour
http://www.kingarthurflour.com/also:
http://www.arrowheadmills.com/ now i'm not sure they are 100% USA because i haven't emailed, but they don't have the international organic symbol on their product

and they claim to be from america's heartland