  We present 2603 spectra of 462 nearby Type Ia supernovae (SN Ia) obtained
during 1993-2008 through the Center for Astrophysics Supernova Program. Most of
the spectra were obtained with the FAST spectrograph at the FLWO 1.5m telescope
and reduced in a consistent manner, making data set well suited for studies of
SN Ia spectroscopic diversity. We study the spectroscopic and photometric
properties of SN Ia as a function of spectroscopic class using the
classification schemes of Branch et al. and Wang et al. The width-luminosity
relation appears to be steeper for SN Ia with broader lines. Based on the
evolution of the characteristic Si II 6355 line, we propose improved methods
for measuring velocity gradients, revealing a larger range than previously
suspected, from ~0 to ~400 km/s/day considering the instantaneous velocity
decline rate at maximum light. We find a weaker and less significant
correlation between Si II velocity and intrinsic B-V color at maximum light
than reported by Foley et al., owing to a more comprehensive treatment of
uncertainties and host galaxy dust. We study the extent of nuclear burning and
report new detections of C II 6580 in 23 early-time spectra. The frequency of C
II detections is not higher in SN Ia with bluer colors or narrower light
curves, in conflict with the recent results of Thomas et al. Based on nebular
spectra of 27 SN Ia, we find no relation between the FWHM of the iron emission
feature at ~4700 A and Dm15(B) after removing the two low-luminosity SN 1986G
and SN 1991bg, suggesting that the peak luminosity is not strongly dependent on
the kinetic energy of the explosion for most SN Ia. Finally, we confirm the
correlation of velocity shifts in some nebular lines with the intrinsic B-V
color of SN Ia at maximum light, although several outliers suggest a possible
non-monotonic behavior for the largest blueshifts.
