Before my group switched to 3.5, I wrote a Microsoft Access program for character creation, adding in classes and other traits as I accepted them into my campaign. However, I have not had the time or desire to update it to 3.5. Most of the generators back then were not customizable and locked users out of the programming. What's the point of a spreadsheet if you cannot customize it?
Now, I use either Mad Irishman's form-character sheets and a MS Word-based character sheet I found somewhere. The Word document is my favorite because it is so easy to expand the box where feats are listed (in the case of fighters), alter the part of the character sheet detailing equipment (some characters might need to have detailed descriptions of unique items and/or effects), or whatever else I want to modify. Adding a watermark in the image of a coat of arms is really easy, for example.