Good free editors in the cross-platform world include vim and emacs. They are both highly programmable, have lots of 3rd party add-ons and provide colour syntax highlighting and tab-completion of symbols and filenames. It's a matter of opinion which is best, and a subject I'll not get into.

A non-free but popular Windows editor is textpad, which might work out for you better than notepad.

On the subject of the unacceptable additional characters, it sounds as though you are either getting tabs into your source files or having problems with Unix/Windows line-ending conversions. Could you provide more details? (Both the free editors above default to including tabs in your source files, but google can tell you how to get them to insert spaces instead fairly easily). It might be better fixing this problem rather than looking for a new editor.

(vi/emacs and tabs/spaces in the same post? /me prays fervently I'm not starting something we'll all regret later).