In the United States today, there are four companies selling insulin.
In the United States, three companies produce the seven insulins for sale for human use (there's also vetsulin).
The seven insulins, in rough order from slowest to fastest are:
Lantus- marketed as a 24 hour steady rate insulin, often the first insulin type 2 diabetics are put on because it is usually given once per day. In type 1 diabetics, it is often used as the basal part of basal-bolus regimens. It has a low ph level that makes it sting. In actual studies, the time that it lasts in a person can be as short as 10 hours, and it hasn't been studied past the first 24 hours, when it's usually still active, and so works for some unknown length of time greater than 24 hours in most people. Also, many users find that it is a little stronger 4-8 hours after injection. Made by Sanofi (formerly known as Sanofi Aventis).
Levemir- marketed originally as a Lantus imitator, which doesn't sting. It seems to last 24 hours somewhat less often, but is for the most part used as though it was just like Lantus. Somewhat more frequently than Lantus, given twice daily. Made by Novo Nordisk.
NPH (Neutral Protamine Hagedorn) - a recipe of insulin plus additives developed in 1946. Its original charm was in being longer lasting than regular. It is visibly identifiable as the cloudy insulin, and most users take it twice a day. It peaks too strongly to be used only as a basal insulin for many people and takes too long to use for bolus; it is something of a combination insulin whereby it provides the background insulin for the day plus the lunchtime insulin. The main drawback of NPH is that users need to eat on schedule. The main advantage is that it is cheap. NPH is available for sale internationally under a variety of names. In the United States, it is sold as Humulin N by Eli Lilly, and as Novolin N by Novo Nordisk.
Regular- this is insulin made by genetically engineered e coli, molecularly identical to human insulin. It is (for most people) the slowest of the insulins used to bolus for meals, for some people not kicking in until an hour after injection and having a tail of action lasting as long as 8 hours. It's cheap. It is sold as Humulin R by Eli Lilly and as Novolin R by Novo Nordisk. It is also available as a concentrated insulin.
I recently switched over to this insulin and was surprised to find that it kicks in for me in under 15 minutes and does not have a tail past four hours (well, maybe five).
Humalog- this insulin has been altered to work a little faster than Regular, and it is almost the same as Novolog. Kicks in in 5-15 minutes, lasts four hours or less. It is used as a bolus insulin. It is made by Eli Lilly.
Novolog- the first of the insulin analogues, this insulin is molecularly altered with the goal of making it work faster than Regular. For most people, it does- kicking in in 5-15 minutes and finishing the job in 4 hours or less, typically. It is manufactured by Novo Nordisk. It is also available as a diluted insulin.
Apidra- the newest of the insulins on the market in the US, marketed as the most speedy insulin for insulin pump users especially. Manufactured by Sanofi (formerly Sanofi Aventis).
Also available are a variety of combinations involving NPH. All of the insulins with numbers in their names are a combination of NPH with something. Novolin 70/30, for example, is 70% NPH with 30% Regular. Humalog Mix 75/25 is 75% NPH based on Humalog with 25% Humalog. There are no real advantages to a premixed insulin and a number of huge disadvantages. The biggest of these is that it's much harder to correct a high blood sugar if you don't have a fast acting insulin that's not attached to NPH.
Eli Lilly has the distinction of having been in the insulin manufacturing business the longest; the company was actually started for the purpose of making insulin within a year of the discovery of insulin. It is based in Indianapolis, Indiana (HQ is visible from the greyhound bus riding in and out of Indianapolis) but insulin is no longer its focus; it is the maker of prozac and cialis, among other drugs. It reported more than 5 billion dollars of profits last year, and has a little under 40,000 employees.
Novo Nordisk is based in Denmark and somehow the artwork on my Novo Nordisk stuff really seems to show that. Nordisk has been in the insulin business almost as long as Eli Lilly (it was started in the same year for the same purpose for the European market) and is the inventor of NPH. Annual profits are over 2 billion dollars and it has roughly 30,000 employees.
Sanofi Aventis is based in Germany, and apparently changed its name to plain old Sanofi more recently than the boxes in the stores reflect. It has over 100,000 employees, and makes more than 6 billion dollars in profits a year.
All three companies have been involved in really shady medical/business practices, including hiding important information for regulatory bodies in ways that probably or definitely resulted in people's deaths. Eli Lilly and Novo Nordisk both have programs in place that provide insulin (among other things) to people living in poverty.
Vetsulin, the insulin marketed for dogs (although probably most diabetic dogs on insulin are being given one of the insulins above) has the distinction of being the only animal (pig) derived insulin still being sold in the US. It is made by Merck and Company, and oddly enough, it's not cheaper than NPH or Regular. It is sold at a more diluted strength.
Merck is headquartered in the US, where it was founded in 1891. It grosses roughly 5 billion dollars per year, with about 1 and a half billion being profit. It has roughly 94,000 employees.