Travelling as a single person is fabulous.......when you travel with someone you tend to ignore everyone around you but when you travel alone you talk to other people and make friends.....which is great.
I'm not a fan of Ibiza or any party-town but Amsterdam is fabulous (cheap flights are readily available)......Madrid or Barcelona are great.....if you want somewhere a little more sophisticated I've heard that Prague is a wonderful place.
If you want to get a little further afield.....Egypt is great and not as expensive as you think if you get a cheap last minute deal. And you can't go wrong with somewhere like New York, nice and metropolitan and a generally funky place to go.....
Hope that helps and that you have a fabulous time.....PM me if you want some more info particularly on Egypt or America.....
I've often travelled alone , it's one of those things you can do as a man that can be a problem for women . It's different to being 1/2 of a couple , it allows you to do a lot more and cover more ground and do it at shorter notice since I don't care if a room I get for one night is a palace or a dump so long as it's warm and dry . Most women like something fairly plush . Now being on holiday for 2 weeks on a beach with a fit girl who boogies your woogie is worh a little effort in picking the hotel !