I adore this outfit on Rihanna. She's the only songstress I know who can pull off literally any kind of clothing. Some days she's goth, with rings strung up and down her fingers and badass knee high leather boots, other days she's sassy and sweet, like the ensemble below.

Lucky for us, Rihanna's look is easy to recreate! Just a few simple pieces are all you need- you probably already have some of these in your closet.

 

For starters, you need the blue button down. This one from Old Navy Boy's section is only $14.50, and should do the trick.
This embroidered cotton mesh mini from MaxStduio is a good alternative for Rihanna's skirt. The detailing is a bit different, but it has the flounce that hers has, and the color is similar. Note: if you're willing to shell out for the real thing, here's the actual skirt RiRi is donning.
This double stranded pearl necklace from Dillards is only $32, and looks exactly like the one Rihanna is wearing.
Last are Rihanna's sandals. Hers are undoutedly super expensive, so I've found a pair that's in the same color scheme. These shoes from Endless.com are a close enough match to get the look, and they're on sale for $40.