There are plenty of greeting card apps for iOS, but this new offering called Lovely Handwritten Cards (free with one in-app option) is tasteful, and lets you truly personalize what you send to others using your own handwriting.
You can choose a template from subject areas like Holidays, Birthday, Congratulations, Love, etc. Add any photo from your photo library, which then can be scaled and/or rotated, then use your finger directly on your touchscreen to add your note. There are a variety of ink effects to make your writing look like your own.
You also get a choice of different ink colors, as well as line thicknesses. When you are done, your card can be printed, or send it via email or the usual social networks.
I think the key word with this little app is tasteful. The templates are nicely done, and you'd have to work to send something that looked bad.
For an additional US$0.99 you can get a bunch of extra templates, and that's reasonable enough, but most of the few included templates are just fine. Templates with a lock symbol require the paid set.
Lovely Handwritten Cards is a universal app. It requires iOS 7 or later, and at free it is certainly worth a look.