Samsung is now the number one Android handset manufacturer in the US market. This is due mostly to their Galaxy S handsets, with flavors on every major carrier. Verizon has the Fascinate (and Continuum), Sprint has the Epic 4G, T-Mobile has the Vibrant, AT&T has the Captivate, Cellular South has the Showcase, and US Cellular has the Mesmerize.
According to Gartner, prior to this quarter (and the release of the Galaxy S line), Samsung accounted for 9.2% of Android phones in the States, but now they make up 32.1% and have the majority stake.
As you probably have heard, the Galaxy S phones are very powerful, each with a 1 GHz Hummingbird system-on-a-chip, 4 inch Super AMOLED display, and a 5 MP camera. There were various other features that some had and others did not.
Personally, I have Bell Canada's Galaxy S Vibrant, but I use it on AT&T (it has the same 3G frequencies).
Motorola and HTC are the runners up, and their options are not paltry. Many of the Verizon Droids are Motorolas, and the flagship phones for T-Mobile and Sprint are HTCs. We know that the Motorola Olympus/Etna is coming soon, in all its dual-core goodness.
It seems that Samsung's non-exclusive marketing model worked really well. If they release the same product (with slight variations) to every seller, they get more products sold. So raise your Galaxy S (or your imaginary wishful-thinking one) in the air, and cheers to Samsung for a hot commodity and awesome device.