Is there a Drupal shopping cart interface for Bitcoin? Is there any Drupal SCI for Bitcoin available? Either tied into Ubercart or, more preferably,  Drupal Commerce.
You could have a look at uc_bitcoin by Mike Gogulski that seems be what you are looking for. A word of caution though: The GitHub code has not been updated since November 2010, it is for Drupal 6.x (has not been tried on D7) and Mike states that "There’s probably not going to be an update for a long while, either, so fork and code away". Anyway, here's some info about it:


  A Bitcoin payment method for the Ubercart shopping cart for Drupal.
  
  Features
  
  
  Generates a new bitcoin address for every order
  Provides payment address to customer on site at checkout, plus in a
  subsequent email
  Configurable timeout after which unpaid transactions will be
  canceled automatically
  Configurable number of Bitcoin network confirmations after which an
  order is considered paid
  HTTP or HTTPS access to bitcoind
  


There is also a project by Darrell Duane that is based on Mike's project. There is no download available yet and the project page was updated in June 2011.