Stayed in one of the two Ibis hotels (Ibis Karlin if I recall correctly) in February - smart, clean and decent food. Only a 5 minute metro from the heart of the city or a little stroll. No frills but reliable. Great city, you'll have fun. Look out for the jackpot prize places (Herna?) every other building
Can't comment on owt central, but the first time I went I stayed at the Hotel Golf which is a 15min tram ride out of the centre, clean, tidy hotel and for £9 a night B&B couldn't moan. Second time I went stayed at the Prague Hilton which was voted the world hotel of the year a bit back, but that was pure class, however min price there is £145 per night. Try www.octopustravel.com for hotels.
Hotel Central Very nice...2 mins from old town square, very clean and not full of stag parties. Went in November and will certainly use the same hotel again.
Yalta Hotel Stayed there in the good old days (1970), excellent in the Commie days, must be brilliant now.
Hotel Melantrich - just round the corner from the Old Town Square but cheap http://www.hotel-melantrich.info/
hotel julian fantastic, quaint place. good food and plenty of beer in the cellar bar. depends what central is. 5 minute tram ride from charles bridge (opposite side to the old town).
depends what you're going for but... ...keep away from wenceslas square. biggest let down - you might as well be in the English toilet that is London..!!!
The link below is to a fairly decent set of apartments I stayed in about 3 years ago - on Wenceslas Square but a bit set back from the main street so not too noisy at night. Very cheap too. And a great pizza restaurant within the building - pizzas cost about £1.50 and were gorgeous. http://www.bestprague.com/
But yeah... Thought the strength of the beds might be relevant Mind I'd have thought Magaluf beds'd be made stronger!