I own their albums Boy, October, War, The Joshua Tree, Rattle and Hum, Achtung Baby, ATYCLB, and HTDAAB, my favorite album being The Joshua Tree, and favorite song--well, it's too hard to narrow it down, but it's somewhere between With or Without You, Electrical Storm, and One.
I'm really glad to have joined this community--U2 fans seem like a sincerely nice group of people!