Stellarium -- A free, open-source planetarium. You can set your location and date & time to see an accurate portrait of the sky. This program also has red mode, so that if you have a laptop, you can take it out with your telescope without worrying about ruining your night vision. This program is available for Windows, Mac OS, and Linux.

TeXnic Center -- An editor and typesetting for LaTeX. If you're using windows, this is all you need to write a LaTeX document and turn it into a pdf.

Stellarium -- A free, open-source planetarium. You can set your location and date & time to see an accurate portrait of the sky. This program also has red mode, so that if you have a laptop, you can take it out with your telescope without worrying about ruining your night vision. This program is available for Windows, Mac OS, and Linux.

Plot 0.997 -- Plot is a scientific 2D plotting program for Mac OS X. Plot is designed for everyday plotting. It is easy to use and creates high quality, professional plots. It allows easy and powerful manipulations and calculations of data, and it is free, so you can't go wrong. Highly recommended.

Papers -- Papers is a program that stores and organizes your scientific papers (or any pdf files) in a very iTunes-esque way. You can add notes to your papers and match them with the versions stored on various databases like ADS and Arxiv.org. You can group papers into categories, making it very easy to keep track of multiple projects at one time.

TeXShop -- Like TeXnic Center (see above), only for Mac OS X. This is all you need to write a LaTeX document and turn it into a pdf.

Stellarium -- A free, open-source planetarium. You can set your location and date & time to see an accurate portrait of the sky. This program also has red mode, so that if you have a laptop, you can take it out with your telescope without worrying about ruining your night vision. This program is available for Windows, Mac OS, and Linux.