Ever since researching while preparing for our wedding in 2007, I have fallen in love with stationary, in all varieties and colours. One place in particular that I love (and where we ended up getting our informal invitations from) is Paper source: http://www.paper-source.com/
Not only do they have a variety of invitations that you can order and print yourself, they also have a variety of other cute (and useful) stationary and paper items.
We used invitations with a similar style to these, for our post wedding party dinner in Christchurch.
And I just love their variety of cute and funky note cards.
The only issue is, last time I checked, that they don't post internationally :(