Ultrafast spectroscopy continues to be a powerful tool for observing dynamics in quantum mechanical systems on the femtosecond timescale, a chemically important time window corresponding to molecular vibrations and many electronic transitions. Exploiting the characteristics of frequency comb lasers, we develop new techniques to overcome limitations of current methods of ultrafast spectroscopy. Frequency combs were developed as a tool for metrology and their use for precision spectroscopy has been widely recognized. However, the utility of a frequency comb for ultrafast spectroscopy is not as obvious. We exploit the properties of frequency combs to improve the sensitivity and broadband detection of ultrafast spectroscopies. One such technique we are developing uses ultrafast fiber-laser frequency combs coupled to external enhancement cavities to increase the sensitivity of ultrafast transient absorption spectroscopy. The enhancement cavities increase the laser power and effective absorption path length, thus giving signal enhancements of several orders of magnitude over traditional transient absorption spectroscopy. Noise reduction techniques improve the sensitivity of transient absorption by more than four orders-of-magnitude over previous best techniques. We can now study dilute samples in molecular beams on the femtosecond timescale with transient absorption spectroscopy, opening up new areas of chemical research. I will discuss this technique and others we are developing that use frequency combs to make significant improvements in ultrafast spectroscopies.