  We present JHK photometry and spectroscopy for a sample of newly identified L
and T dwarfs from the Sloan Digital Sky Survey (SDSS) and known dwarfs from the
SDSS and the Two Micron All Sky Survey (2MASS). Spectral classification has
been carried out using four infrared indices; we identify 9 new L8-9.5 dwarfs
and 14 new T dwarfs from SDSS, including the latest SDSS dwarf yet found, the
T7 SDSS J1758+4633. We classify 2MASS J0415-0935 as T9, the latest and coolest
dwarf found to date. We combine these results with previously published data to
produce a sample of 59 L dwarfs and 42 T dwarfs. We compare the near-IR colors
and absolute magnitudes of dwarfs near the L-T transition with predictions made
by models of the distribution and evolution of photospheric condensates. There
is scatter in the spectral indices for L dwarfs, suggesting that these indices
are probing different levels of the atmosphere. The near-IR colors of the L
dwarfs also scatter, likely due to variations in the altitudes, spatial
distributions and thicknesses of the condensate clouds. We identify a group of
late L dwarfs that are blue for their spectral type and that have enhanced FeH,
H2O and KI absorption, possibly due to an unusually small amount of
condensates. The scatter seen in the H-K color for late T dwarfs can be
reproduced by models with a range in surface gravity. The variation is probably
due to the effect on the K-band flux of pressure-induced H2 opacity. The
correlation of H-K color with gravity is supported by the strengths of the
J-band KI doublet. Gravity is closely related to mass for field T dwarfs and
the gravities implied by the H-K colors indicate that the T dwarfs in our
sample have masses in the range 15-75 M_Jupiter, except for SDSS J1110+0116
which possibly has a mass of 10-15 M_Jupiter.
