To date, I already visited the city of Barcelona on 2 occasion (both were 1 week stays), and I still believe that there are many attractions which are yet to be explored. I will definitely revisit soon, since I simply fell in love with the place. If you are planning to visit Barcelona (or thinking about it) here are some cool tips from a travel junkie.
Visiting the old part (Barri Gothic Area) of the city is a must-see, yet in my opinion, the best parts of Barcelona are its contributions to 20th Century architecture.
One must definitely visit all monuments left by famous 20th-century architect Antonio Gaudi; Parc Guell, Casa Miro, Casa Batlo, and most of all, the famous, unfinished Sagrada Famiglia Cathedral.
Other definite monuments to be seen are the Palau de la Musica, The Maritime Museum, Picasso Museum, The Olympic Complex, and for the best nightlife of all, the Olympic Village.
Day Trip Suggestions:
I would typically suggest a trip to Salou, where one finds the magical theme park of Port Aventura. We spent 2 nights in the resort which adjoins the park, and booked this directly via the Internet . When I tried booking via my agent it was going to cost me 15% more. Hence, simply book this yourself since its very easy to do so.
Arriving to the destination, is very easy since the resort and the theme park has a station located only 100m away from it. Whilst, Port Aventura may not be as large as DisneyLand Paris in size, I personally feel that it has a certain atmosphere of adventure which the Parisian park lacks.
Other day trips worth considering are a visit to the wonderful Montserrat Mountains, as well as a visit to beautiful seaside resort of Stiges. You may acquire very advantageous day trip packages which include transportation, museum entrances, and lunch at the Tourist Information Office.
Besides buying a good guide book (DK has a very colorful and informative guide), I would suggest that you would log onto the Barcelona Tourist Information office website, and contact them asking for some literature. For a very small charge (probably less than 3 Euros), they will send you very useful maps and guides which will definitely help you in planning your trip.