The one I use most often is Google's dictionary:

https://www.google.com/#q=define:hello%20world

Where did they get an arbitrary 154 calories for a pint of beer? Calorie count is closely tied to style and alcohol content. A few examples:

Bud Light: 109 calories in 120z. Dogfish Head 90 Minute IPA: 294 calories in 12oz. Weyerbacher Merry Monks: 279 calories in 12oz.

There's a link below the results that says "sources include USDA" and points to http://ndb.nal.usda.gov/ndb/foods/show/4166?qlookup=14003&ma...

Probably the same source Wolfram Alpha uses.