I have always wondered if there is a wider significance to Harlequin and Columbine in Act I of the Nutcracker. The original Hoffmann story does not seem to give specific details of the dolls at the party (he does seem to have a love of mechanical dolls...) so I wondered if they have their own story, like Princess florine and the Bluebird in Sleeping Beauty or represent something in particular?

Lexie,

They are two characters from a form of traditional Italian theater called Comedia del Arte. This goes back several hundred years and there were various plots that involved these two as well as some other traditional characters. The costumes and clown makeup are part of the tradition.

I'm drawing a blank on coming up with any but they probably appear in other ballets. They also pop up in opera, the characters appear in I Pagliacci as well as Ariadne auf Naxos among others.

From wikipedia:

http://en.wikipedia.org/wiki/Commedia_del_Arte

Hope this helps

comedia characters were popular throughout europe, as the tradition of this initially improvised theater with its stock characters spread beyond italy.
i suspect they were suggested by petipa to tchaikovsky because they were popular and familiar to the russian public.
eventually petipa would choreograph LES MILLIONS D'ARLEQUIN and subsequently the charactes would become russified in the fokine/benois/stravinsky collaboration for PETROUCHKA, where petrouchka and the ballerina doll are heirs to both harlequin/pierrot and columbine. i don't think these particular characters appear in THE FAIRY DOLL.
the other NUTRCARCKER dolls, as you likely know, were a sutler (canteen keeper) and cavalry soldier. i suppose all of these were popular choices for christmas-present dolls throughout europe.
(these thougths come from the top of my head, i assume wiley's TCHAIKOVSKY'S BALLETS would shed some light on all of this.)

And don't forget that the original idea was to have two devils who appeared out of a snuffbox, intended for the minor mode music after the present-day Harlequin/Columbine waltz. Cooler heads prevailed; no terbacky for little kids' parties!

Thanks!