I have used these sublingual lozenges for a while:
http://www.seekinghealth.com/active-b12-lozenge.html
They seem to be well absorbed, even too much for my taste!
I got lots of anxiety with these at around 800-1000mcg with adrenaline surges that have been very unpleasant to say the least. The same doesn't happen with Metafolin taken orally, even @2000-2400mcg.
My very non-scientific interpretation is that they absorb too fast and they hit my nervous system too quickly. I have noticed the same problem with fast dissolving B12 tablets vs those that dissolve more slowly. The former typically give me some anxiety.
cheers