Joanne,
I do them in 2 ways.
Firstly, I went to Tescos and bought a pack of blank cards with matching envelopes in a pack of 50 - approx £8.
I then went into WORD and customised the measurements of the whole card.
I then put in 2 columns to distinguish both sides of the card, ie front cover back cover, (turn card over and inside left inside right).
I then use a suitable pic, eg heart for valentines, type in a message. On back cover type in my T&C and address.
Inside I type a little message. I then add the same pic but smaller onto the corner of the envelope.
This works out very cheaply and you can customise for any occassion. Also, if people give me enough notice I can type in a personalised message and add the person's name.
Second option:
go into vistaprint, find NOTELETS, use those as gift vouchers. I choose my pic, type in gift voucher on front cover. I then pay extra for the inside to be in colour too, and add another personalised message, 'Just for You' or something on those lines. It works out about £7 for 10. (You pay extra for the envelopes to have pics on so I don't bother).
With vistaprint you can download your logo, but pay a ONE OFF fee to do that, but then can use that logo over and over again on other items without further charge. think its about £2-3 one off fee.
Extentionize has also kindly sent me a gift voucher template with my logo on. So will probably use that somewhere too.