There are currently many genetically modified crops in use or underdevelopment - this is currently not an exhaustive list.
Liberty Link crops have a gene that makes them resistant to the herbicide glufosinate, also known as Liberty.
Roundup Ready crops have a gene that makes them resistant to the herbicide Roundup.
Improved Nutrient Content
Golden Rice is a transgenetic rice that has several genes that allow it to accumulate Beta-Carotene, giving the rice grains a yellow orange color. Beta-Carotene can be metabolized in humans to form vitamin A. Golden Rice is considered to be a humanitarian project because it can provide adequate amounts of Vitamin A to millions of people whose diets consist primarily of rice and are deficient for this nutrient. Golden Rice is not currently in use, but field trials and breeding programs are underway to develop varieties of the rice that are adapted to local growing conditions.
Virus resistance papaya
Sunup and Rainbow are two similar varieties of transgenic papaya that are resistant to the papaya ringspot virus (PRSV resistant papaya). These two varieties express a viral gene that encodes of part of viral protein coat. It is believed that the expression of the viral gene leads to RNA silencing of the viral gene during infection and hence makes the virus incapable of replication.
Bt crops have a gene from the bacteria Bacillus thuringiensis that produces a protein that specifically kills the larvae of certain insects. Bt strains of corn, cotton, and soybean exist and are currently in use.
Improved Shelf Life / Post-Harvest Characteristics
The Flavr Savr tomato was the first transgenic crop produced and commercialized. The tomato has a antisense gene insertion that downregulates production of an enzyme that causes break down of the cell wall during ripening. This modification gave the tomato a longer shelf life. The Flavr Savr is no longer in use.
The flesh of apples (and some other types of fruits) will brown when exposed to oxygen. An enzyme called polyphenol peroxidase is responsible for this reaction. A transgenic apple was developed called the Arctic Apple that has little or no polyphenol peroxidase activity and thus undergoes less browning when exposed to oxygen.