It is important to note that only eight crops are currently available as GM varieties in the United States: alfalfa, canola, cotton, corn, papaya, soybean, some squash and sugar beets. Also, you referenced GM wheat, but there is no GM wheat in production in the United States. Here is a table outlining what year these crops became available commercially:
Upjohn (now Seminis)
Cornell University/University of Hawaii
Monsanto and Forage Genetics
Monsanto and KWS SAAT AG
This response from Dr. Bob Goldberg, professor in the Department of Molecular, Cell, Developmental Biology at UCLA, discusses the fact that there is no genetically engineered wheat grown anywhere in the world. Additionally, Dr. Brett Carver, Regents Professor and holder of the Wheat Genetics Chair in Agriculture at Oklahoma State University, clarifies the fundamental process by which new wheat varieties are created in this response.
You might want to check out this table from the U.S. Department of Agriculture, which shows biotechnology petitions for determination of non-regulated status.
If you have any additional questions, please ask at http://www.gmoanswers.com/ask.