i like Notepad++ because it is quick to start up, can support many languages, and it can even match a <div> with the </div> so that you can check when a <div> is matching the correct closing </div>...
but it seems like it is missing the feature of having a left side panel of folder and file browsing (and for easy opening). Is that true? Can it actually do so?
I was after this Notepad++ plugin myself (but didn't know it name, big thanks to musicfreak) and also found that version 5.4.3 does not ship with Explorer.
So saving you time and Google energy consumption here's the link to the Explorer (and other excellent) plugin(s) http://sourceforge.net/projects/npp-plugins . This install method is deprecated: Please note AntonioCS comment below.
Then simply drop the .DLL into your install path \plugins (eg x:\Program Files\Notepad++\plugins) folder and restart Notepad++.
In Notepad++ 5.6.8, I was unable to find the explorer plugin in the plugin central page in the project's wiki, unzip the unicode version, put the dll into the plugins directory of Notepad++, then restart Notepad++. Then go to Plugins -> Explorer -> Explorer. It's not exactly like TextMate's "mate ." within Terminal.app to open a directory and its files (which I'd love to have in Notepad++ or in any decent lightweight free Windows text editor), but it works. Thanks much to Jens Lorenz for the plugin!