Corneliani suits come from a good quality Italian fashion house. They even make clothing for some well-known American brands.
They offer a wide variety of menswear but their suits are their most well-known offering. They are known as one of the finest Italian designers, not quite as good as Canali or Kiton but definitely on par with a Zegna. They have a pretty traditional Italian cut. You'll get medium padding in the shoulders, good for a taller, athletic guy.
In years past American brands such as Polo Ralph Lauren outsourced some of their nicer more expensive suit lines to Corneliani. They have a great reputation within the industry.
Much like the American makers, they created three labels with different price and quality:
Corneliani - This is the top-level mainline. You'll get fully canvassed and nice quality fabrics. This is probably the best value for them, and one of the best values you'll get for a suit anywhere.
Trend - This is their "trendy" line. More flair than the more conservative main line. You'll see browns and white pinstripe type designs for instance.
CC Collection - This is their cheapest line. You'll see these in discount stores such as Marshall's from time to time.
Some fashion mavens claim that there is a Sartoriale line that's even better than the main label, but I have yet to see this in person.
Bloomingdale's and Saks Fifth Avenue both carry some of the mainline editions, at least in their New York stores. If you are in Europe, you can visit a company store and use their made to measure service. Most of these go for about $1500 or so retail but they'll go for about half that in the department stores. For $600-$700 its a great bargain for a fully canvassed suit with nice Italian craftsmanship. For more delicate fabrics, such as Super 200s, you can easily spend up to $3000 retail though.