Black denim is very trendy right now. I personally have a faded black pair that I've been obsessed with for a year.
For a casual look, pair them with plaid tops and flat boots. Concert tees with them. Grey sweaters. Button down shirts and a scarf.
For a dressy look, pair them with a sheer black top, cami and killer heels. Neon is huge for spring and it looks great against black denim (think electric blue, hot pink, bright raspberry). Silver and gold beaded tops look awesome against black denim too!