I would also look at Meego (what Maemo became after it merged with Moblin), which you can code in C, C++, or Python (or really anything, although the native graphical interface is Qt).
The only issue with either of those is that you might be writing an app that no one will use (as one platform was still-born, and the second isn't yet born). That's the price you pay to avoid learning new technology though.
http://arstechnica.com/open-source/news/2009/06/android-goes...
You can also cross-compile iPhone apps on Linux, however, you won't be able to sell it at their app store.
Another alternative is the Nokia N900 which uses maemo.
It's not seamless, and you might need to learn Objective-C (don't worry, it's not Java), and you can't submit to the App Store, but it is possible.
If the "lightly hacked" part gets in the way, you can even debootstrap a real Debian release onto the device and develop in that.
The hardware is decent as well; it certainly feels more solid than the HTC slide phones I've played with recently, and despite dropping it a few times it's barely got the shine worn off after 8 months.
All that being said, it's entirely unclear what the future of the platform is; Meego could sink without a trace in 6 months, and I don't know if Nokia are planning a successor device. In my mind they'd be insane not to, but sanity hasn't been Nokia's hallmark of late.
Having said that, take a look at Appcelerator's Titanium (appcelerator.com) or AppMakr (appmakr.com). They both provide tools that enable you to create HTML/CSS/Javascript screens and also intermingle with other scripting languages to produce a compiled app for desktop, Apple, Android, and others.
For instance, if your app is intended to go into widespread distribution and make you some money, then the answer is either Android (suck it up an learn Java) or IOS (you should be able to develop on a Hackintosh).