For investors who aren't fully convinced that the U.S. is on the cusp of a jobs boom, On Assignment ( ASGN) is a more conservative play. The company provides staffing in health care, biotech research, engineering and other niches that aren't economically sensitive. That focus is what the company calls the "math and science" niche. Management tends to downplay expectations as evidenced by the fact that On Assignment has topped EPS estimates by at least 14% for four straight quarters. This staffing firm will release quarterly results on Feb. 14, and if history is any guide, an upside surprise may be in the offing.