Zenit has a neat story on the Vatican accepting donations for Peter's Pence online.
Here's the website. One can mail donations in. Or fax a credit-card number over. Or give online. [Or, oh how dreary and mundane, give to the second collection whenever it is taken up.]
The neat thing? The server on which this page resides is called "isidoro.vatican.va" [Isn't that your patron, Izzy?]
Though, frankly, putting a check in the mail and addressing it to His Holiness Pope Benedict XVI has a certain thrill about it ...