There's The Linux Action Show which isn't an Ubuntu specific video podcast exactly, but they do cover everything that's new in the Linux/Unix community in general (and there's something happening to Ubuntu quite often these days).
It's a weekly show which is being recorded live every Sunday. Every monday the show (+- 50 minutes) is delivered through rss and available on their website in every format you'd care about.
Topics range from Linux gaming in general, to reviewing Ubuntu 10.10 and derivatives like Mint.
They do have their own opinion and are (sometimes painfully) objective and stick to their own principles. If you can handle that, you're bound to appreciate their sense of humor.