look on this thread http://www.ibiza-spotlight.com/phpbb/viewforum.php?f=5&sid=
There are loads of good places. Check out Kasbahs by Kanya and Coastline, walk round the bay, down by the marina.
Just avoid the ones that all seem to have the same menu and a board with pictures of all the various things thjey serve with chips and salad.
Go to Ibiza Town too.
Unless you want "British" food, in which case you need to be a little bit more adventurous. The seafood is good at the nicer places because it's all fresh, and I'm not particularly in to that sort of thing.
And you have to remember that a lot of the San An places are very cheap, and there is a difference between cheap and in-expensive. Because there are some good, in-expensive places.