Holly Madison -- Best Birthday Planner Ever?

Being Holly Madison's assistant has its perks -- and this week in Vegas, Angel Porrino got a b-day even Hugh Hefner would approve of.

We're told Holly threw Angel a daylong party at TAO Beach before chowing down on sea bass, crispy tuna and loads of sushi at TAO Asian Bistro ... all while sippin' on champagne.

Angel then got a ginormous five-tiered, "Harry Potter" themed cake when the party moved over to TAO nightclub -- naturally -- for the rest of the night.

Not bad for a 21st b-day, right?