Visualforce and Apex Theme for Notepad++

The only combination I'm aware of at the moment for a text editor is Sublime Text 2 and Maven's Mate.

Sublime Text 2 is cross-platfrom (as opposed to TextMate which is Mac only), super fast, and has a lot of really fantastic text productivity features, such as multi-line editing.

Maven's Mate gives you some of the major features Eclipse, such as deploying to the server when you save, and some initial auto-complete. It's still got a ways to go, but the deploy to server on save has been enough to make the switch for me. Note that Maven's Mate doesn't officially support Windows, but has a pull request which provides an alpha version.

Another alternative is to use Eclipse to manage pushing data back and forth to Salesforce and using Notepad++ (or any text editor) to edit the files. After you're done edit just go back to eclipse, right click the project, and select refresh (the eclipse refresh, not the force.com refresh from server). When you refresh the project the eclipse auto-build will automatically save it to the server. In practice I'll do the major refactors and editing in the text editor, and then correct typos in Eclipse since the save failures will link to the line number.

Do you plan on using Notepad++ to edit the code and then push it to the server with Ant scripts or something? I'm curious how you plan on getting the code back to the server. Also, what about the added benefit of the Schema Browser etc?

I'll be the first to admit that the IDE has its problems, but I've never found a better solution.

As a backup plan if there is nothing available, you may be able to build something custom with Notepad++ (I'm not sure if it supports extensions/addons) using the Tooling API.