I feel like I hear だべ all the time (through TV and on the streets of Yokohama where I live), but I'm wondering about it's origins and modern usage.
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It's Tohoku dialect.
Basically, だべ is だろう, 行ぐべ is 行こう. There are a lot of variations though, as you can say for example だすっぺ for でしょう.
I doubt though that your hear that a lot on TV, except during interviews of people who suffers from the tsunami or nuclear accident. And it would be subtitled anyway…
Edit: Ok, so it seems that だべ is in fact an "coastal" ending. This is why your heard it in Yokohama, while in didn't where I lived. It's used all along the Pacific coast, and is thus not restricted to Tôhoku. I do not know, though, if they use べ without だ as in the examples I gave.
I believe べ is the equivalent of the volitional in some, usually considered rural, northern dialects.
For instance, いぐべ = 行こう (with a systematic voicing thrown in for a good measure) of Miyagi-ben.