Sky Charts/Maps and Object Lists
There are a wealth of online references for the amateur astronomer. Here are a few to get you started.
Monthly Star Chart
Astronomy and Astrophysics in the New Millennium
SEDS Messier Catalog
Interactive Messier Catalog
SEDS NGC Catalog
Interactive NGC Catalog Online
SBIG Astronomical Instrument
The STScI Digitized Sky Survey
Clear Sky Chart
Clear Sky Charts are charts showing factors such as clouds and humidity that affect observing, arranged by time of day. The color scale goes from white (bad) to dark blue (good).