There are some really good companies in the coaster industry.
B&M- Good company, very smooth and enjoyable roller coasters, shame they aren't unique every so often. Nearly half the rides they have built are clones.
Intamin- A really innotive company, they always try more unique things, like there accelerators all differ from each other, they have also made some other nice rides like the Half Pipe, their SLC's, and there amazingly cool Ball Coaster.
Arrow- Used to build some amazing coasters, shame they have gotten rough over the last few years, but they had some amazing ideas for rides, like Drachen Fire, launched roller coasters, 4D roller coasters, the Fishook rides.
Vekoma- The most recognisable name in the industry, mainly because of there amazingly cheap and easy going roller coasters, very famous for their Boomerang roller coasters, they have continued to impress people with the invertigo's and the Vertigo Boomerangs. Many good ideas for the future like the Tilt roller coaster.
Maurer Sohne- Now there's a name that's getting recognised fast now after they have brought out their X-Car roller coasters. They make some interesting rides, like the spinning wild mouses and there Xtended range of spinning roller coasters.
Schwarzkopfs- The gods of roller coasters, the only company in the world to ever use a continous loop. Just shows how good a company they are. Anton Schwarzkopf never liked to use OTSR's and always tried to put lapbars on his roller coasters. They had some interesting ideas for the future, like the worlds first true flying roller coaster.
Guesterlar- My favourite, because they have such a wide selection of rides to choose from, they have the spinning roller coasters, the typhoons, the launched roller coasters, it has soo much to offer now. I can't wait to see what they will pull off in the future.