I haven't played too much with Wolfram|Alpha (the name's rhythm and the buzz about which remind me of "Keyser Söze") yet, but here are a few things I like so far:
--enter a color word--for ex., "ochre"--and you get a swatch, the 24-bit RGB values, the HTML hex code if there is one (also "nearest named HTML colors" hex codes) and swatches of "complimentary colors";
--enter the name of a school--for ex, "Oberlin College"--and you get its location on the map, info about when it was founded, enrollment and annual degrees awarded by field stats, accrediting agency, and link to the school's website;
--enter a date and the response includes, among other things, how many weeks and days ago it was (I'm 1,815 weeks--or 12,705--days old today. You?);
--enter a number of words--"5000 words"--and get back how many pages they'd amount to in a single-spaced or a double-spaced document (also the data size in MB "assuming 8-bit-coding"); and
--type in a word (in English--"manzana" gave me the unit of measurement, not the apple) and get the definition, synonym suggestions, pronunciation, and--here's the sweet part--frequency of occurrence in writing and in speech ("based on the 100-million-word British National Corpus").
I found these via trial and error, before noticing the Wolfram|Alpha examples page, which gives a much better, much quicker picture of what W|A can and can't do [grin]. Also of interest to library types might be the Wolfram|Alpha Community page, where users post what they'd like to be able to do with Wolfram|Alpha (you can subscribe to the feed).