When most investors think of "under the radar" stocks, they generally believe those stocks are not well-known because they have small market caps. But Hilary Kramer, editor of GameChangerStocks.com, has come up with two stocks that are relatively unknown, but have market caps in the billions of dollars. A third stock is a small cap stock.

Among her picks is Optimer (OPTI) -- a small cap stock -- but one that is a potential takeover candidate by big pharmaceuticals. Optimer, says Kramer, has a drug that fights infections that patients often pick up while they are in the hospital.

Another stock Kramer recommends is Parexel International (PRXL),a contract research organization, which serves biotech and pharmaceutical companies by handling their marketing and drug trials. The company has made big inroads into China where this could be a $12 billion industry.

Kramer also says that Brookdale Senior Living (BKD) is a good buy. This is a play on nursing homes and patients with illnesses such as Alzheimer's. Only 10% of this company's reimbursements come from Medicare -- so it's really a private insurance play.