Alghero is very nice, a marina and then beach further down, very old town center with lovely restaurants and bars. Not too lively unless you want to find somewhere. Plenty of nice beaches further around the coast and they do some boat trips to a nice cave on the coast.
http://maps.google.co.uk/maps?hl=en&ie=UTF8&ll=40.572696,8.308067&spn=0.044398,0.109177&t=h&z=14
This is where we stayed, a nice 1 room apartment in the old town center. they have some others in the town so you should be able to find something.
http://www.aigua.it/en/loft/loft.html
Alot of B&B’s in Italy are not really B&B’s. They will leave you some juice cartons and snacks for breakfast but the cafe’s are so cheap and plentiful that it’s nicer to go out for brekko anyway.