I know some things about many of these could be helpful;
Above Ground Level- mainly the old element discs molds with a few new ones added, all molded by Gateway as far as I can tell.
Aqua Flight- owned by Sun King, molded by gateway. All light weight to float.
Birdie Disc Golf Supply- new company just one mold so far
Cheengz- from GA, mainly catch/dog looking discs in heavier weights.
Crosslap-German company went slide the for a while but is now back at it.
Disctroyer-from Estonia, pretty good quality I've tried their Skylark mid. It smells like silly putty but throws well.
Divergent Discs- from the Philippines, targeted to new and lower powered players.their silicone Alpas putter is interesting.
Elevation-compression molded rubber discs, WAY floppier than vibram
Finish Line Discs- Drew Gibson's new venture
Fourth Circle Discs- from Australia, I think Innova molds them though
Full Turn- I think they have shut down but had a couple of cool molds
Galaxy- from China, quality is decent.
Guru- from Norway I think, mainly aimed at new players
Kaufinator- Legacy discs with coffins on them. I think you get a prize if you ace with them and can prove it.
Launch- from the UK and they have awesome glow plastic rhatton is involved.
Lone Star- my sponsor! Making high quality discs in Houston, they do other injection molding and got into DG a couple of years ago. Pretty strong growing lineup.
Nite Ize- discs with lights built in, I don't think they have ran any in a few years.
Sky Quest- makes a few interesting discs, but I think they might be shut down.
Storm- another one molded by gateway.
XCom- Chinese manufacturer aiming at newer and low powered players