Computing Exposure Times with the IRAF Task CCDTIME [2]
ISPI Exposure Time Calculator [3]: for ISPI infrared imager on Blanco 4-m telescope.
SMARTS Imager Exposure Calculator [4]: for 0.9-m CCD and 1.0-m Y4KCam
Object Visibility [5]: ING utility which plots altitude against time for a particular night (Staralt), plots the path of your objects across the sky for a particular night (Startrack), plots how altitude changes over a year (Starobs), or gets a table with the best observing date for each object (Starmult).
Links:
[1] http://www.ctio.noao.edu/noao/content/Astronomers-Tools
[2] http://www.noao.edu/gateway/ccdtime/
[3] http://www.ctio.noao.edu/instruments/ir_instruments/image_cal.html
[4] http://www1.ctio.noao.edu/noao/content/smarts-imager-exposure-calculator
[5] http://catserver.ing.iac.es/staralt/index.php
[6] http://www.ctio.noao.edu/misc/astro-links-new.html