Punchbowl

Punchbowl is a free website that allows you to send digital cards and invitations.

Via

Their selection of eCards is quite extensive. Each category has free eCard options and paid eCard options. The free ones are actually cute, unlike some other "free" sites you may opt to use.

Although you can use Punchbowl for free, the free version limits you to 10 cards per month, and I believe you can only have a maximum of 10 or 12 recipients per card. {Bummer.} The other levels of Punchbowl membership obviously cost money, and you get more features the more you pay:

Comparison plan found here

Each level comes with a 30-day free trial.

Users have the ability to send an invitation {complete with RSVPs and reminders for people who RSVP yes} or plain cards {with the option to include a gift card}.

Here's an example of a digital card I made at Punchbowl {click any picture to see the animations on your screen}:

I'm thinking this would be a great way to thank parents, volunteers, and PTO members -- no postage or expensive Hallmark card required.

Punchbowl Features:

• Lots of free card designs
• Several categories of eCards: birthday, thank you, just because, apology, good luck, holidays, graduation, anniversary, congratulations, thinking of you, sympathy, get well
• No trip to the store, $5 card, or postage necessary
• Ability to send a gift card with your eCard
• Change the digital postage to a design of your choice
• Change the stamp on the outside of the envelope
• Change the envelope liner to something cute and matchy
• Ability to customize text inside the card
• Ability to import e-mail addresses from your mail account
• Plan an event from start to finish -- such as parent/teacher conferences, classroom parties, field trips, etc. Allows you to send digital invitations, RSVPS, etc. 

P.S. This post goes into more detail about how to send an invitation, and this post reviews how to send a digital card through Punchbowl.