If you purchased a Nexus 7 before Google announced its price drop, Asus has you covered. As TabletGuide first pointed out, the manufacturer is distributing €30 Asus store vouchers (₤25 for UK customers) for those who bought one before October 29th. Only customers who purchased directly from Asus
or Google are eligible, however, and you must register your device with Asus and provide your proof of purchase. We confirmed with an Asus spokesperson that the offer is valid for all of Europe, but we've yet to hear about a similar program in the US. The application period ends on November 30th, and the voucher is valid through December 31st.
Update: Google is also currently offering price protection for those that purchased a 16GB Nexus 7. If you bought the tablet from Google on or after October 14th, the company will refund the $50 difference to your account.