Today's a big day for celebrity birthdays with three reasons to celebrate. Gossip Girl's Blake Lively turns 23, Rachel Bilson's ringing in the last year of her twenties at 29 and Alexander Skarsgard is embracing his true sexiness at 34. Rachel kicked off her celebration over the weekend vacationing in a bikini while Buzz also has a sneak peek of her return to HIMYM. Blake's been busy filming, but hopefully she'll take a break to party with friends and her PDA loving boyfriend Penn Badgley. Alexander Skarsgard has been overseas with his girlfriend Kate Bosworth, though he'll be back in LA by this weekend to present at the Emmys. So, tell us — which of these celebrity birthday bashes would you most like to attend?