What’s on Tonight: Gaga on ‘Idol’

American Idol (Fox) — The last time Lady Gaga appeared on “Idol,” she performed “Alejandro.” This time around, she serves as mentor to the final four contestants as they sing… the songbook of in the 1930s and wrote hit songs in the 1950s? Screw you, Fox.

Modern Family (ABC) — Nothing from its second season made our list of the best episodes of the 2010-11, but that doesn’t mean “Modern Family” isn’t still excellent. It’s just reliably solid every week, consistently clearing a comedic bar that most sitcoms only achieve on their best days.

South Park (Comedy Central) — Trey Parker and Matt Stone tackle the royal wedding. Should be a good one.

Extreme Couponing (TLC) — Coupon clipper Amber’s shopping trip hits a snag when the babysitter cancels, forcing her to bring her four children to the grocery store. Over/under on the number of dirty looks she gets from other shoppers: 300 million. (Watch a preview clip here.)

NBA Playoffs (TNT) — A pair of Game 5s: Celtics-Heat followed by Grizzlies-Thunder. I got roped into that triple-OT Game 4 the other night and didn’t get to bed until after 1:30 a.m. Stupid Russell Westbrook.

LATE NIGHT GUESTS: Attractive people alert! Jon Hamm and Miranda Kerr are Conan’s guests tonight. Less so on Letterman, who has Chaz Bono. Also on the docket: Dick Van Dyke on Leno (holy sh*t, his audience is ancient); Chris O’Donnell on Kimmel; Tim Meadows on Ferguson; Keith Richards and Paul Bettany on Fallon; and Albert Brooks on “The Daily Show.”