You can also connect to you N900 over (local) network with ssh (you can use Putty for this on Windows) and use a CLI editor (vi, vim, nano,...) with a big window on you computers screen + real keyboard to edit the files on your N900.
Python is very good since it is well integrated in the system, if you need to do faster programs then you need to download and install scratchbox and work with C ( =Gnu C Compiler )
I'd suggest C++ and Qt/QML.