If Hallmark cards and other mainstream greeting companies are too unoriginal with their wording for your taste, try Wiki-style e-card web site PigSpigot for witty e-cards that cover birthdays, holidays, and more.
Touting themselves as the "anti-Hallmark with a wiki twist," PigSpigot lets you search and send e-cards for free. The site also offers the option to send free Tweet cards, as well as greetings sent via snail mail for $3.99.
If you don't like what you see, you can always design and upload your own card. Browse the full link for all the e-card selections, and if you still can't find something you like, check out previously mentioned e-card site someecards to help get your message across. (Note: PigSpigot contains some potentially NSFW cards.)