i'm sure this thread will get overwhelming for the OP- many points of view, many will contrast, ext.
so i'll just repeat other peoples ideas that i agree with
-octave pedals. a really good sounding -1, clean, +1,+2, all with independent volume controls would be sick. good tracking and a musical sound, a warm natural sound, not a digital icepick. i'd buy one. who else??
-filters. its true, there are never enough in the world. keep an eye on what pedals have become popular, give respect to the classics, but be unique!
-even though i will contradict myself here, you SHOULD build your take on a good fuzz. there are many suggestions above as to what that would be. i just dont like hearing of new pedal companies, and going to their webpage (willing to spend money on products i like!) to find nothing but two generic sounding dirt pedals and a clean boost. that said, if you're a self-respecting pedal builder, whats you're fuzz? my own tip on the fuzz (and again, im sure this exists all over the place) is something with a clean blend, and a switch to effect the low end of the fuzz itself. blending a clean signal with a not to bassy fuzz is cool, but also having a 100% wet signal and loosing no low end. also, this would be a fuzz for guitar players too.
-synth. yeah i said this already, but for me- a big fan of synths- the only one i ever used happily was the Korg G5. i would gladly buy another if the time ever came. the EHX is too hard to actually use at a gig. the deep impact is very cool, and does have its moments, but on the whole is a cheep digital sounding pedal. the markbass doesn't seem to have gained much popularity, though i hardly used it. chunk systems octavius had huge hype and now i dont ever hear about it.
and more importantly, when can we expect to see your products available for purchase? us TBers are quite impatient..