Is there any other query that triggers Google Calc and shows the answer above the search results and not in a separate page, other than:

[the answer to life, the universe and everything] ?

Here's one: [40 rods per hogshead]

http://www.google.com/search?q=40+rods+per+hogshead

Interesting. I wonder why are these queries special?

Compare this then...

[days per month] (with search results)
http://www.google.com/search?q=days+per+month

[days in month] (without search results)
http://www.google.com/search?q=days+in+month

Also:
[e] http://www.google.com/search?q=e
[e-1] http://www.google.com/search?q=e-1
but not
[e+1] http://www.google.com/search?q=e+%2B+1

And [minutes per hour] doesn't trigger the calculator whereas [minutes in hour] does.

The results for [minutes per hour] are terrible.

[speed of light]
[speed of sound]
[mass of Earth]
[calorie]

What about currency?
http://www.google.com/search?q=1EUR%20in%20USD&sourceid=navclient-ff&ie=UTF-8&rls=GGGL,GGGL:2006-10,GGGL:en