I have another suggestion (or two) for you to consider:
If you use a clapboard or other visual to sync audio, you could record it separately to a computer if you have one in the same room. With a USB-Mic, you could eek out the higher resolution audio and do a lapel (sp?) mic, and then route that into a USB Audio Interface, then record into an app like Audacity, or directly into your NLE (whatever you’re editing on). Then, you can sync the audio in post-production, after bringing in the video into your editor.
Another option is getting a dedicated audio recorder to simultaneously record the audio feed. Zoom makes some pretty nice ones that are low-cost and high quality. If you go this route (“dual system” as it’s referred to in the industry), then make sure the formats are the same and the sample rate and bit depth match, or else you’ll have sync problems when you go to edit.
That may be more than you’re willing to do though, but I think that’s the only option if you want to go with the Flip.
Another really interesting option is to stay Standard Definition but go with a higher-end audio solution. I recently researched and recommended the Zoom Q3
to someone who was planning on doing podcasting. The audio is superior to the audio on the Flip, and for static videography (stationary where you’re not doing a whole bunch of moving video) then you don’t necessarily need HD, especially if the distribution is going to be on the internet (not broadcasting on TV or DVD distribution). If you YouTube Zoom Q3 you’ll see some demo videos that people have recorded, where the video is not bad, but the difference in audio is night and day.