Character Tools:
Math and bookkeeping are the "hard" parts of being a GM.  Oh, and remembering rules, what spells are going, the magic ring that Fizbo was wearing that adds to his defense against Land Sharks, etc...  These tools can help.  If nothing else, they can sure help you get a character created quickly.



Game System

e-Tools Developed by Fluid for Wizards of the Coast, e-tools is a more advanced version of the character generator that was included in the first release of D&D 3.0.  It needs to be patched to make it really work well.  Codemonkey Publishing has taken over development.  Now data packs are available for D20 Modern and D&D 3.5.  It includes all the monsters and races from the core three books by default, and the 3.0 data set.

One big advantage to this program is the way it integrates into the mapping program Dunjinni.  It can export its character as XML content that can be easily imported into adventures designed in Dunjinni.  Familiarity with both programs can make generating a professional looking (as in "looks like you bought it somewhere") adventure the work of just a couple of hours.  Its monster generator and battle-block printouts can make a GM's life a lot simpler. 
D20, D&D
PCgen Open-Source meets Open Gaming License in this terrific little product.   PCGEN is free, and comes with the data sets that are part of the D&D SRD. There are commercial data sets that contain products such as D20 Modern & D20 Future, and these are released by Codemonkey Publishing.  PCGEN is a powerful tool, and the character sheets it makes are very nice.  But its output is not easily used with mapping programs.  See the current SRD here. D20, OGL
GURPS Character Assistant The GURPS Character Assistant is a complex toolbox which generates excellent character sheets for your GURPS game.  It is not as intuitive as it could be - a "wizard" would be nice -  but it is comprehensive, and has features such as "Campaign" global settings and job templates that make a GM's job easy when s/he has to generate several characters.  My biggest complaint is that it doesn't have tools to auto-generate NPCs. GURPS
Character Sketcher From the makers of Fractal Mapper & Inspiration Pad comes the Character Sketcher.  If you can't draw, or can't draw on a computer, or can draw but don't have a scanner, this program can help give a general idea of what your character looks like.  (Sample) Any
Faces On the other hand, if you want to make your character look like a professional Police-Sketch artist did the picture, you might consider using Faces software.  It'll set you back $150 for the educational version - but if you have disposable cash and a lack of art skill it'll do. Any