Yes, generic versions of Zyrtec are available. The patent for Zyrtec expired in 2007.

Zyrtec (cetirizine hydrochloride) is a nonprescription antihistamine. It is used to prevent or treat symptoms of hay fever and to treat cold or allergy symptoms such as sneezing, itching, watery eyes, or runny nose. It is also used to treat itching and swelling caused by chronic urticaria (hives).

Generic Zyrtec is made by many different manufacturers including
Actavis Elizabeth
Apotex Corp.
Caraco Pharmaceutical Labs
Dr. Reddy's Laboratories, Inc.
Mylan Pharmaceuticals, Inc.
Par Pharmaceutical, Inc.
Perrigo
Ranbaxy
Sandoz
Wockhardt USA.

Generic Zyrtec comes in the following strengths and forms:
Cetirizine 5 mg tablets
Cetirizine 10 mg tablets
Children's cetirizine 5 mg chewable tablets
Children's cetirizine 10 mg chewable tablets
Children's cetirizine syrup, 1 mg per mL (5 mg per teaspoonful).

Not all of the generic Zyrtec products have been called their usual "generic" name, "Cetirizine". You can check if a product contains generic Zyrtec by looking for "cetirizine hydrochloride" in the active ingredients section of the package label.

Because non prescription products are regulated differently to prescription medicines FDA equivalence ratings are not assigned to generic Zyrtec products. Therefore, it is difficult to say with certainty that a "generic" non prescription medication is completely equivalent to the brand-name product.