There are few d20/Pathfinder character generators. I found some based on Excel spreadsheets which is crazy weird to me.

There is Hero Lab which not only costs money ($30) but for additional book support you pay $10 to $30 per set (so you can get the core rules with Hero Lab base [it comes with one ruleset of your choice] + $10 for Advanced Player's Guide + $10 for Advanced Race Guide + $10 for Ultimate Equipment + $10 for Ultimate Magic... it adds up pretty quick). And I'm guessing you can't add your own data sets which makes Hero Lab quite expensive unless you play one game system a lot.

That leaves PCGen, a d20 character generator that also supports D&D 4E and Pathfinder. It's free and open source and the community adds rulebooks constantly.

Advantages

1. *free
   

2. *Windows, Mac OS X, Linux/Unix
   

3. *wide support, active community
   

Disadvantages

1. *it's a Java application, you must have a JRE installed
   

2. *it's kind of ugly (because it's Java and they don't do much customization for OS X though there is a System Look skin so it's not amazingly ugly)
   

3. *a few bugs, some undoubtedly dependent on the Java version you're using
   

PCGen has some guided access. Level up and it'll give you a list of things you need to do (get spells, skills, feats, etc). There are lots of tabs and sub-tabs so information is everywhere and can get confusing finding exactly what you need.

Pretty much all SRD/PRD text is in there so you don't need to look at the rulebook for descriptions. You load rulebook sets and each character remembers its rulebooks. This way you don't deal with rules you'll never use.

There are a dozen or so toggles for house rules and failing that you can change your stats, hp die roll and create custom magic items.

PCGen highlights things in red if you don't have the prerequisites. You can then click on the item to read the description and see what prerequisites you are missing.

Overall PCGen is a pretty complete character generator. It lacks ease of use and ui polish and it can be slow but it beats spending $100.