Man, that question takes me back! 'Rosario + Vampire' was one of those anime that really got me into the supernatural school genre back in the day. The mix of comedy, action, and harem elements was just so much fun. Sadly, as far as I know, there hasn't been any official announcement about a third season. The second season aired way back in 2008, and the manga actually went in a much darker direction later on, which the anime never adapted.
I'd love to see a reboot or continuation that follows the manga's more serious tone, kind of like how 'Fruits Basket' got a proper remake. The original anime deviated quite a bit, especially with its more lighthearted approach. Maybe if there's enough fan demand, they might revisit it someday. Until then, I'll just keep rereading the manga and dreaming about what could've been.