I don't mind e-cards. Paper cards are getting pretty expensive these days; and I have several relatives and friends that simply can't afford to send gifts and cards out for every birthday or holiday that rolls around. E-cards don't offend me at all. Many of them are super cute. Besides it's the thought that counts really. Cards are used to express something; remembering a birthday, holiday, etc.
I think the only situations where e-cards would be lacking in class would be if someone just passed or if you need to send a traditional thank you for say, a wedding gift or something like that.
In terms of what site, I was using Blue Mountain for a bit. It's been a while since I've been back there. Some sites charge small yearly fees to use their site, others are free. Just google e-cards and it should give you several options.