I also used to hate the Dragon Ball series, but after watching it, I was hooked (well, sorta; the action was a little too intense at times and overwhelmed the plot
). My favorite part of the series was the Cell Saga. I liked Android 18 because she was sexy and deadly.
Other than that, I can't really think of an Anime that I used to hate, but I can think of quite a few that I hate now, but not before, namely Poke'mon. From '98 to 2000, Poke'mon was cool, but it lost it's touch I guess because it became too juvenile for me. I still have all the cards, but I'm only hanging onto them for the money.
An Anime I never liked at all was the Thundercats. The animation, plot, characters, voice actors, everything sucked IMO.