I had been trying to add some spices earlier but didn't have much success with most so I have abandoned the idea (not getting any younger). Most of what I looked at were plants tagged with "pepper" in the name (regardless of whether or not in the genus Piper). As Peter points out, black pepper (P. nigrum) is a good crop. I tried to find some clonal varieties of pepper here but had no luck. (The selected commercial clones are typically hermaphroditic and have been selected for flavor and/or disease resistance.) Even if you plant seed from a selected hermaphroditic clone, it is typical that some portion of the seedlings will revert back to dioecious plants. I abandoned black pepper when I was not able to locate any good clones (I wanted to have very good quality black pepper, not just "Hawaiian grown" black pepper).
I also looked at some other Piper species used as spices. These would have the same issue (dioecious) but there are probably no select varieties of these so seed seemed the only reasonable option. Most of these were Asian / S.E. Asian: chaba, cubeba, longum, peepuloides. An African one, guineense, is also supposedly very good (some claim better than nigrum). Seeds were hard to come by for these & germination was not generally very good when I did find them.
I also looked at various tropical "Sichuan peppercorns" (Zanthoxylum) from S.E. Asia. These include species like Z. armatum (alatum), nitidum, rhetsa (limonella), avicennae, and acanthopodium. Not all produce the same flavor profile as those from the Sichuan region but all are used as spices. There is also at least one from Africa used in this way, tessmanii. There is a snag with these, they are citrus relative so special treatments are required of the seeds to make their entry into the US legal. If you find those imported as spices, they will probably not germinate. You can get a special exception for these in your small lots of seed permit but it requires that the seed undergoes a special treatment prior to being sent to the US (I don't recall the treatment off hand but I had no luck finding seed for any of these, never mind anyone who would do the treatment if they had it). You can probably find the more traditional species (from China / Korea / Japan region) but these would be subtropical or temperate so not sure how they would grow & bear here.
Another one I looked at was an African spice called grains of selim or Negro pepper (Xylopia aethiopica). The pods of this are used as the spice and are typically dried with wood fires, giving a smoky flavor in addition to peppery heat. It seemed that smoking with different local woods might also give an opportunity to craft different flavor profiles in these. I did have seeds of these sent from ForestHouse in Cameroon but there was a problem with the shipment (USDA put my physical address rather than mailing address on package when forwarding) so the shipment was lost.
I don't know if you would be interested in any of these but I think that they would be worthwhile spice crops for here in HI and something unusual that chefs might be interested in playing with.
John