HP is still the big seller . .
. . and last time I looked by a pretty good margin, but the profitable part of the business is selling overpriced inkjet cartridges for very low end printers and suing anyone who refills or makes clones. They still sell the most laser printers, but that distinction is fading fast.
Lexmark (formerly IBM Selectric division) is #2. Dell has entered the printer business with the intent of undermining the others on consumable pricing, and theirs are all manufactured by Lexmark.
Lexmark gained fame by suing a company that bypassed their ink cartridge "blow on empty" chips under the DMCA (Digital Millenium Copyright Act), but as a legal expert pointed out, for due diligence they just had to try it and see if it worked.
For color printing at significant speed, Xerox seems to have it. I haven't seen a laser speed color printer that wasn't a Xerox for at least 5 years. The printers (solid ink) were Techtronics. Good thing Xerox took over because Techtronics was pulling a Banyan, making it as impossible as possible to qualify to sell their product.
For low end dot printers, don't under any circumstances buy a Panasonic (difficulty getting repaired). Okidata and Epson do well for low and midrange.
A bit higher up, I (and Rose) love our Datasouth Documax (there's one hiding under the counter at most airline ticket offices I understand). I have several clients I've sold a couple of them to each (dual track, ours is single track). For multipart forms, though, you have to tell them to go slower on the feed or they'll rip '4m to shreds. Unlike most dot printers you can tell them that sort of stuff.
