Amadeus - The Music Hotel
We stayed a couple of nights in October of 2005, in two different rooms. The staff is very helpful and very friendly and, if you don't speak Spanish, most of the desk staff speak very good English. Value for money is very reasonable - it's in an excellent location (a short stroll to the cathedral and Alcazar, and you're pretty much tripping over restaurants everywhere), with lovely rooms, for 40 Euros less than the similarly located and similarly sized room we stayed at in Barcelona. And it's got waaaaay more character. The 7 Euro breakfast is a pretty typical European breakfast (better food than some: croissants, buns, oranges, cheese - but really awful coffee) which IMHO, is a thing best avoided (go down the street, find a bar, and grab a cafe con leche and some tostada with tomato and olive oil for 2 Euros).
It's an older building, and in some ways the rooms are well-worn (old floor tiles, the odd bit of broken trim, etc), but everything was clean and well-appointed.
I would absolutely recommend this hotel, and it would be my first choice should I stay in Sevilla again.
Unique Quality: Our first room was a Standard Double, and it came complete with a piano (room was soundproofed). Our second room was a Junior Suite, and it was big, beautifully furnished, and had three windows overlooking the street. The lobby has gorgeous tiling, a piano, a harp, books on music and art... There's a music library too. Breakfast, should you choose to risk it, is served in the pretty lobby or on the roof terrace which has great views.