Here is one of them - a Designer Series Envelope made using the Twitterpated DSP from the Mini:
The envelope is pretty enough that a simple notecard is all that you need to put inside:
The flap is secured in place with a small framelit, popped up on dimensionals.
You can make these envelopes in any size. To work out how large your piece of DSP needs to be, take the length of your card and add 3cm; multiply the width by 2 and add 3cm. Eg for a 12cm x 10cm notecard, your DSP would need to be 15 x 23cm. For an A5 folded card (14.8 x 10.5cm), your DSP would need to be 17.8 x 24cm
To make it into an envelope, in portrait orientation, score 1cm from each side. Put your card in the middle but slightly more towards the top and score above and below it. Cut off the top 2 corner pieces. Round the top 4 corners if desired. Fold the side pieces in and apply tape to the lower flap to form an envelope.