Google updated its support pages with an interesting item recently. Down at the bottom of the gift card page, is a US-only option called "Google Play credit gifts." And sure enough, a new option to send a gift has popped up in the web Play Store. So, just in time for the holidays, you can give the gift of Google Play via email.
Gift cards for Google Play have existed for ages, but the option to send a gift directly via email is new. It's accessible in the Play Store sidebar as "send gift." You can send credit in the amount of $10, $15, $20, $25, $50, and $100. Simply fill in the email, and a code will be dispatched. You can also attach a personal message to the email.
This can only be done with real money, though, not any Google Play credit you might have attached to your own account. There's still a separate link in the Play Store to add credit to your own account too. Remember, this is only available to US users right now, but I imagine it will roll out elsewhere in time like gift cards did.