Two you already mentioned elsewhere:
- Craig Eliason (Ambicase Modern)
- Cuttlefish (Antherton Cloister)

One that I'm not sure has an appeal outside the specific habitat (Fontstruct), but has the guts of trying:
- Neurone Error (http://new.myfonts.com/foundry/Abneurone_Trauma_Types/)

How about Ed Fella (and likely a few others of the Emigre gang)?

Good candidates.

Also: LettError (Beowulf, Twin Cities)

And at the subtle end of the spectrum:
Bloemsma (Legato), except he's no longer with us.

I hope I'm getting my drift across (it's not so easy).

hhp

All my non-commissioned types, except perhaps Nicholas/Goodchild, are speculative.
But I wouldn't consider myself a doyen—at least, not until I’ve been profiled in Eye magazine.

I think Panoptica is speculative. Plus it has the bonus of being a
working font too! I say that because that's not a requirement here.

hhp

Wim Crouwels New Alphabet surely. He's still with us.

If you are searching for people on the cutting edge of experimental or 'speculative type' design...

I would include 'andrew byron' as just such a person.

He certainly pushes the boundaries of type design and opens up our imagination to look at things in a different way.

I like his stuff.

Not very marketable, but some of his ideas would make for an interesting font.

In fact, I think I've seen type designers mimicking some of his ideas and stuff recently.

http://www.designboom.com/weblog/cat/8/view/8293/experimental-type-by-an...

And here is an interesting link to experimental type design, compiled by Luc Devroye.

http://luc.devroye.org/experimental.html

And here are some really interesting images... ouch, that's got to hurt!

http://www.fastcompany.com/pics/3-d-typography-experimental-type-designs...

Oh yes, I know Andrew personally - awesome stuff.

hhp

Could Erté be considered a precursor? http://www.erte.com/alpha.html

Also Luc(as) De Groot did some interesting experiments: http://www.fontfabrik.com/lucfuse.html

Imre Reiner

Claudio Piccinini