WHICH OF THESE DESCRIPTIONS BEST FITS YOUR BEER CAN?
If your beer can is a Milwaukee Brand Premium or General Pulaski ...

You have a 1970s novelty item, and not a genuine cone top can... not even a beer can, per se.

Beer can collecting really took off in the late 70s, and these were made as collectible items for beer can collectors at the time.  Neither can is even remotely valuable -- don't be fooled into paying more than a couple bucks for one of these.
Art's Beer Cans
It's not a Milwaukee Brand Premium or General Pulaski, but has essentially the same dimensions...

You have a High Profile Cone Top.  If the bottom is flat, it's an American Can Company product dating from 1938 to the early 1940s.    For a better estimate of date manufactured, refer to the CANCO Patent Dating Chart.

If the bottom is concave, it's either a Continental Can dating from 1937 to the late 1950s, (near the seam of your can is "Cap Sealed), or an American Can can dating from 1941 to the early 1950s (near the seam of your can is "Keglined" and patent numbers).

For a guide on spotting the differences between Continental's and American's high profile cones, click here.
If your beer can is a cone top, but the cone seems shorter than those pictured above...

You have a Low Profile Cone Top.  These were made by the Continental Can Company, from 1935 to 1941.

If the cone has inverted ribs and a flat bottom, it was manufactured before April 1936.  If it has raised ribs (or no ribs) and the bottom is concave, it was made between the Spring of 1936 and just after America's entry into WWII.
If your cone top beer can looks a lot like the strange creation pictured on the right...

You have a Crowntainer.  This was the second design by the Crown, Cork & Seal Company, from 1940 to the early 1950s.

Depending on which collector you ask, these are either the coolest cans ever to exist, or the absolute ugliest beer cans created.
If your beer can's cone seems like a Low Profile, but its spout is unusually long...

You have a J Spout.  This was the first beer can design used by the Crown, Cork & Seal Company, and was made between the years 1937 and 1942.

With the exception of the Old Topper Snappy Ale can (pictured here), J Spouts are quite rare.
www.Breweriana.com
Boston Beer Cans
Click here for an excellent RustyCans.com web page
Superb web site dedicated to Cone Tops
Crowntainer Central
The Rogalski Borthers' web site
Museum of Beverage Containers and Advertising
www.BeerCans.org
If your cone top beer held a quart of beer, and...

   it resembles the shape of the can on the left, your beer can was made by either the Continental Can Company (Cap Sealed panel, below) or the American Can Company (Keglined panel, below), at some point after 1937, but before 1955.
...it resembles the can on the right,  
you have a "Snap Cap" quart can, made by the American Can Company sometime in the 1950s.
Tavern Trove
--OR--
One of my favorite beer can sites!