If you are budget-minded (or just don't care for luxury and extra services but a nice place to sleep) and look for an hotel in the very center of Seville, then Hotel Ducal is your choice. It has only 2 stars but rooms are spacious, staff is nice and you are 5 min walking from monuments like the Catedral or the Barrio of Santa Cruz. And in August they have special offers.

Hotel OK if you not expecting much Room was large, clean and centrally heated and there was a decent sized bathroom Shower was nice and hot Clean towels every day although not very fluffy Not for couples wanting a romantic weekend away as beds are about four feet apart Staff on front desk not the friendliest I've ever met but very efficient Overall OK but I've stayed in much better for not much more money

touble hotel, construction on your floor (or directly above) starts at 7:30am with no prior warning, no airconditioning though promised, shower is almost ok... the staff is poor too..

Acceptable accomodations for a budget traveler. I stayed there on a trip while studying abroad in 2007. Coming from a very "posh" part of London, and used to typical American standards, we were a little startled but able to make it work. Ducal seems to be the standard style for Europe budget hotels.
Roomier than most, with roomy bathroom as well. Tile floors which are good for cleanliness; no "frills" - no tv, no hairdryer. Fresh towels every day, but not sheets.
"View" of a small courtyard/the fire escape :( Can be loud at night, and noises from within the building (people walking and using the elevator) never ceased.
There is a great tasting, cheap cafe across the square, so we never tried the breakfast offered. Be warned - there is a lot of construction going on all over the city as of 2/2007, which was disappointing. Location was good, and we felt safe enough walking back to the hotel around midnight - use common sense, of course. Better locations to be had nearer the Cathedral where we spent most of the days.
There was a slight issue with the desk attendant demanding that he keep our passports upon arrival - of course we refused, but he insisted on holding the copies we had with us instead. When asking for the copies before departing, it took over 15 minutes and a lot of chaotic panic to locate the passports. Don't hand anything like that over to them for "safekeeping," save yourself the trouble.
Overall, definitely visit Seville - our second favorite city in Spain!
Pleasant Travels!