The senate in Madrid just voted to trigger article 155 of the Spanish constitution, which allows them to cancel the regional government. That should stop tax money flowing... I could only find an article in Spanish as it only happened a few minutes ago: http://translate.google.com/translate?hl=&sl=es&tl=en&u=http... Edit: Looks like the BBC has updated the article to include this now.
Actually, that is one of the central demands by catalans: money should not "flow" to Catalonia via Spain.