Previously I use EditPlus to code my WordPress themes. The coding process was a lot easier than using Notepad because I can do the undo process up to multiple levels, it supports syntax highlighting and also it will automatically backup the file whenever you click the Save button.
However after I found out about Notepad++, I fall in love with it. Notepad++ is a freeware text editor which I can say, it is the best Notepad replacement that supports several programming languages and also a good competitor to EditPlus. Notepad++ is written in C++ and uses pure Win32 API and STL which ensures a higher execution speed and smaller program size.