Update, March 19: I've added a few more suppliers to the list, and broken out a third category for the mixed reviews. And I note in the comments that someone claiming to be Kathy Yu from 3B Chemicals is threatening me with legal action. The IP address resolves only to AT&T Internet Services, but there does appear to be someone from that name who works at 3B. I hope, for her sake and that of the company, that this is someone impersonating her, because whoever is leaving these comments is doing 3B no favors.
And since I am reporting opinions, both my own and those of other contributors that I have no reason to doubt, and am doing so without malicious intent, I will cheerfully ignore all legal threats.
OK, here are the lists of good companies and not-so-good companies, based on my experience and those of readers. I've had some personal communications, too, which I've added to the data set. As more reports come in, this will be the post that's updated, so it can serve as a reference.
I should note up front that I'm not listing the Big Guys, since (while they can have their ups and downs), you generally know that they're going to send you something. What we're looking at are the companies that you might not have dealt with, but want to know if they're reliable. And that brings us to the:
ABCR: good prices and hit rate on orders. Very professional.
Activate: expensive, but what's there is there, and it's the right stuff.
Adesis: not cheap, but very reliable and willing to work with customers to deliver similar compounds.
Advanced Chem Tech: recommended for peptide/amino acid stuff.
AK Scientific: several good reports on availability and purity.
Alinda: have ordered one thing from them, which was fine.
Anaspec: good reports on reliability
Apollo: good stuff, but catalog needs to be a bit more in line with their real stock.
Array: very pricey, but it's all there.
Astatech: good experience reported
Bionet: interesting catalog, doesn't back-order you.
Chembridge: a big catalog, but it's all real. Occasional purity problem.
Chem/Impex: good hit rate on availability. Some questions on their chiral purities.
Combi-Blocks: good list of useful intermediates, delivers on them.
Enamine: similar to ChemBridge in many ways. Big catalog. Not the fastest out there.
Florida Center for Heterocyclics: occasional purity issues, but they do deliver.
Frontier: great source for boronic acids and the like.
Life Chemicals: have had good experiences with compound purity here.
Lu: good source for custom peptides.
Matrix: interesting catalog, which they will really ship to you.
Maybridge: on the border of being one of the big guys. Very reliable.
Midwest: good reports on reliability.
Netchem: custom synthesis, but (for once!) with good turnaround and purity.
Oakwood/Fluorochem: good prices and reliability.
Peptide Protein Research: good for custom peptides.
Pharmacore: good stock of intermediates.
Rieke: reliable, only game in town for many odd reagents.
Strem: well known for quality inorganics and organometallics.
Synquest: used to be PCR. Good customer service.
Synthonix: stuff is in stock, customer service is responsive.
TCI: has always delivered, and quickly.
Transworld: very reliable and responsive.
Tyger: have never had a problem with them.
Waterstone Chemicals: good experience on pricing and availability
American Custom Chemicals (ACC): several tales of bad purity and customer service, but others have had nothing but good experiences with them.
3B Chemicals: "will lead you on for months". Several bad experiences reported. On the other hand, I've just heard directly from a colleague who's had good luck with them.
J&W Pharmlab: bad experience reported (delays and purity), but others OK.
Ontario: one good report, but others complain of availability and leads times.
SPECS: mixed reports, but overall positive.
The Not So Good:
Ambinter: seems to source a lot of stuff from mystery suppliers. Many delays.
Any supplier, sad to say, with "Hangzhou" or "Shanghai" in the name. Tend to have absolutely nothing on the shelf, and if there's even a listed price, it's science fiction.
Anichem: very bad experience here with unexplained delays.
Beta Pharma: bad experience reported.
ChemMaker: very negative report on customer service and responsiveness.
City Chemicals: several bad experiences reported
Combi-Phos: several reports of purity problems.
Rarechem: haven't come across anyone with a good report here.
UK Green: a bad experience reported.
Uorsy: nothing ever seems to be in stock.
Zelinsky: several bad experiences reported.