Obviously, with the rise of retro in computing, today there are lots of Z80-based machines in the retro market. Thus, I would exclude anything later than maybe 2005 or obviously targeted at the "retro-market".
What I'm looking for is what was the last Z80 general purpose desktop that was in the market later than the late '90s and neither a "niche retro product" nor an "appliance", but rather something that you could expect to do "serious work" with? For now, my take is the Amstrad PcW16 of 1996 that used a 16MHz Z80 that Amstrad was trying (with not much success) to sell.
Even if "Anne" (its code name) was a very interesting computer - Looked like a Macintosh, had a 16MHz Z80 and Flash ROM for permanent storage and IBM-AT-compatible 3.5" floppy and all external ports (serial, parallel, mouse and keyboard) compatible to AT standards.
EDIT: Some people seem to think the question is unclear or attracts opinionated answers . Maybe I thought this was obvious, so let me try and clarify this a bit:
The gist of the question basically is "How long did the Z80 provide enough uumph to be able to at least somewhat compete on the standard low-cost desktop market with the growing PC competition". The Z80 (or alikes, or its legacy) survived quite a bit in the Handheld Gaming market, that we all know, that is why I have limited myself to the desktop. It also survived for a long time in "appliances", that is why I wanted to exclude them for the same reason. While I do acknowledge that my above example is borderline "appliance", you could still run standard CP/M on it. I'm perfectly willing to accept such niche products as long as they help answering the gist above.
I excluded "retro" for the same reason that such products wouldn't answer my core question. You can decide yourself: If the designer thought there'd be a market for his new product because there was a Z80 in it, it's likely retro and excluded, but if he thought there would be a market for it even though there is a Z80 in it (or his customers wouldn't even care), then it's likely not.