Next year, I will definitely be using the NetPost service offered by USPS. It is a simple way to send a regular snail-mail letter from your computer/browser via USPS
There is the postage charge, and then an additional $2 per “run” or per letter. It makes sense if you are sending the same letter to everyone, like, say a wedding invitation.
For stuff like Greeting Cards for occassions, you can create your own from a picture, or choose one from their gallery. And yes, you can send Gift Cards from a whole variety of retailers.