Personally, I'd say Prague is one of the only cities that rivals Paris when it comes to romance and charm — and it's got chimney cakes (also known as trdelník, a doughy, rolled dessert that's reason enough to fly to the Czech Republic). Sugary treats aside, Prague has all of the breathtaking bridges, castles, and old-world allure that any couple could ask of a weekend retreat. Flights start at about £35, and the city's also got its fair share of high-end, low-cost hotels, like the MGallery by Sofitel (rooms run about £80 a night).
(PS: Keep an eye on Google's LastMinuteTravel feature and you might be able to snag a room for as little as £4! Yes, really.)