I know exactly what this is. I had this with my first pregnancy and have it again NOW with my second. I also gag and dry heave because of it contantly, and vomit if I attempt to swallow it. I have to sleep with multiple towels. During the daytime I carry a spitcup constantly at home or paper towels in public. The only thing that I find helpful when around other people is to snack on salty popcorn, pretzels, and/or to drink constantly. Unfortunately plain water tends to make me gag because I can "feel" the saliva in it. Yuck!
It's called ptyalism (sometimes misspelled ptylism on the internet ) and its truly a terrible experience during pregnancy. It is rare. Rare enough in fact, that in my doctor's office, of which there are 5 ob/gyn's, I am the first patient they actually had with it. According to my ob, she studied it in med school YEARS before but I am the first she's had. That being said, even though its very rare, you aren't alone out there. I know of one other person who had it too. I went through it for 7 months (I believe)with my first pregnancy and for this one - I am 13 weeks and hoping to God it doesn't go that long this time. Unfortunately, since its so rare, there isn't really medical research or ways that I know of to help it.
I very recently saw on a message board discussing it that someone recommended "ipecacuanha" (a homeopathic solution) but I haven't seen my doctor yet to ask about it. Here is a link of discussion about ptylaism:
http://www.mothering.com/discussions/showthread.php?t=273591
Good luck to you. If you hear of anything that would help, please pass that back to me.