Yeah,
Rotterdam still is, kind of. It is more spread out now, with most gabbers coming from small(er) villages, but well...
Most of the new Dutch electronic music still comes from The Hague and Rotterdam, but maybe I'm being a bit of a regionalist
If you want more core-ish music check out
http://home.wanadoo.nl/liquid28/diskonext[1101]%20-%20No%20Alibi.mp3 but I guess you already listened to that one? (sorry phpBB doesn't support [ and ] in [url] tags.)
-diskonext