Notepad++ is a program I've used a lot lately, both at home on personal projects as well as in professional work. Major features include tabs for all of your files that persist between sessions, a session manager that saves your tabs so you can switch between projects easily, syntax highlighting for quite a large number of languages, a macro system, an extensive plugin capability and much more.
I have two plugins that I use constantly. One is the compare plugin which will compare two files and show you differences between them. It can also compare a file to the last saved version of itself. This is very handy for seeing what changes have been made and can be used to normalize multiple revisions of a file.
The other plugin that I've started using fairly recently is the NppFTP plugin. It allows you to connect to sites that use ftp, ftpes, ftps, or sftp and read/save text files directly from within Notepad++. I've used this in my recent website work to edit the files directly on the webserver and then preview in my browser without having to do anything about copying files back and forth. One of the nice things is that with a very minimal configuration I can work remotely on my netbook just as well as on my main desktop. I currently have it configured to use sftp via ssh on my website development box which is an old Dell desktop running Ubuntu Server 10.04.
If you were to setup your router to let you access ssh and www externally then it would be possible to develop on the road.
The downside of NppFTP is that it is only good for editing files with Notepad++, you can't actually use it to transfer files like PDF, WAV, etc with it. At least, unless you use uuencode and somehow uudecode it on the remote end. I use coreftp to transfer files but you could use Filezilla or another client that supports the method you want to use such as sftp.