There are few things you have to bear in mind when deciding on your stationery:
Budget: decide how much you can afford to spend overall, then break it down to a cost per invitation. Don't forget to include postage costs in this.
Information: How much are you putting in the invitation? You'll need the basics; names, time, date and
venue, how to reply. Do you want to give guests directions to the venue and other extra information? If so, then think about whether you want it on insert cards, which will increase the cost (but looks lovely) or if you're happy to do this separately, for example on a wedding website.
Website: If you're having a wedding website remember to include the address and password on the invitation.
Think about the style of your wedding and the colours you've picked and what kind of invitations will compliment them.
Samples: If you're looking at online companies always order samples - the picture on the website may look lovely but you want to be sure the quality will match.
Other things to remember include timescales (how far ahead to order, when to send the invitations out), the number of invitations you'll need (it's one per household, not one per guest) and proof-reading; always get someone who hasn't been involved in any of the stationery ordering to look at your proof before confirming with the stationer.
But hey, we all know that this blog post is really just an excuse to gaze at mouth-wateringly lovely stationery. Below are designs from my favourite wedding stationers, although it wasn't easy narrowing the choice down - they're just too pretty!