Inkscape

Inkscape is a vector graphic editor similar to Illustrator or CorelDraw. Inkscape is better in the sense of cost because it is free. It is also an open source software. It can be downloaded for free at http://inkscape.org/ The nice feature is that graphics can be saved in pdf format. It allows high quality graphics when you use it with pdflatex to produce pdf files. Since they are Scalable Vector Graphics, unlike bitmap images, there is no problem even when they are magnified.

The following is an Inkscape example to draw a line with arrow head. 1. Select Bezier Curves tool. Click to start a line. Double click (or click then press enter key) to end the line. 2. Click Fill and Stroke... command under Object menu (or click Fill: or Stroke: near lower left corner). In the Stroke style tab, change End Markers to arrow. 3. Line color can also be changed in Stroke paint tab. Click Extensions->Modify Path->Color Markers to Match Stroke to change the arrow head color also. To insert math symbols, you can press ctrl+u and type the hexadecimal Unicode code point of the symbol in a text box. Then, press enter.

http://wiki.inkscape.org/wiki/index.php/FAQ
http://www.unicode.org/charts/PDF/U0370.pdf