It's a car company under Toyota's corporate umbrella.
It's a Toyota. It's basically an Echo with "hipper" styling. For $12,600 MSRP, with Air, Power everything, and a Toyota build...you can't go wrong IMHO. It's the poor man's MINI. 
Poor man's mini. Heh, considering the original mini was an economy car....
FYI, yes, Scion is Toyota. Just like Lexus is Toyota. It's a marketting thing. The US in general thinks of japanese cars as either economy cars (like the toyota corolla/tercel, nissan sentra, mazda protoge) that are rather boring or decent family cars like the toyota camry, nissan altima, madza6. Most people don't think luxary, sports, or tuning when it comes to those except for Honda Civic and Accord since there are a billion aftermarket parts for those. Granted this is a perspective in the US. All over the world they have different images. Such as the Acura NSX is known as the Honda NSX everywhere else. The Lexus IS300 is a Toyota Altezza everywhere else.
Obvioously there are a few exceptions, like the Mitsubishi 3000GT VR4, Toyota Supra and Mazda RX7/8 have made there way over here as a pretty decent sports car. But you don't see something like the Nissan Skyline over here unless it has been imported. You also don't see anything like the Toyota Celica GT4, except now that rally racers have become a little popular and we now have the Suburu WRX STi and Mitsubishi Evo.
Personally I'd love to see some european cars come over here but not in a chevy or ford shell. I'd love a Peugot 306 with WRC body kit and Opel Speedster. Glad to see Lotus bringing the Elise over here with a Toyota Celica powerplant

In the US you mainly think Ford, Chevy, Dodge. Toyota and Honda have been doing a pretty damn good job of taking the market as accord and camry are the number one and two selling cars. But outside of those names we don't see much. In fact, since Ford, GM, and Daimler Chrysler own most of the car companies (look at their corporate websites), anything one of them thinks might work well in the US that they are selling elsewhere will come over here but under a current well known US name, like Ford, Pontiac, Chevy, Dodge.