We booked a 1/2 day tour with Barcelona VIP Tour, www.barcelonaviptour.com.
Our guide, Abel, is an art expert and extremely knowledgable about his city. Abel was recommended to us by the Artes Hotel concierge and I can also highly recommend him!
The office phone is 00(34)937657814. There is so much to see in Barcelona, it ireally is best to start with a guide. Then you can explore in depth on your own if you prefer.