This letter utilizes composite spectral energy distributions (SEDs) constructed from NEWFIRM Medium-Band Survey photometry to constrain the dust attenuation curve in 0.5<z<2.0 galaxies. Based on similarities between the full SED shapes (0.3-8 micron), we have divided galaxies in 32 different spectral classes and stacked their photometry. As each class contains galaxies over a range in redshift, the resulting rest-frame SEDs are well-sampled in wavelength and show various spectral features including Halpha and the UV dust bump at 2175 Angstrom. We fit all composite SEDs with flexible stellar population synthesis models, while exploring attenuation curves with varying slopes and UV bump strengths. The Milky Way and Calzetti law provide poor fits at UV wavelengths for nearly all SEDs. We find a strong correlation between the best-fit slope and the bump strength, with steeper laws having stronger UV bumps. Moreover, the attenuation curve correlates with the specific star formation rate (SFR), such that galaxies with higher specific SFRs have shallower dust curves with weaker UV bumps. There is also a weak correlation with inclination, which may be suggestive of a two-component dust model. A varying grain size distribution, as a result of differences in UV radiation fields may also contribute to the observed trends. Our results have several implications for galaxy evolution studies. First, the assumption of a universal dust model will lead to biases in derived galaxy properties. Second, the presence of a dust bump may result in underestimated values for the UV slope, used to correct SFRs of distant galaxies.