* American Idol (8 pm/ET Fox)
The epic sing-off signs off in tonight's Season 8 finale. It's been a zigzaggy, sing-songy journey - a four-month, spaced-out odyssey that rocketed through the preliminary auditions (remember Bikini Girl?), the Hollywood rounds, catty group performances and the cuts at the judges' mansion. (Got drama, Tatiana?) Over 100,000 hopefuls auditioned this season, and it all comes down to the Top 2 and the crowning of either Kris Allen or Adam Lambert. On tap is a big pop celebration with special performances, surprise guests and a reunion of the Top 13. From the Nokia Theatre L.A. Live.
* The New Adventures of Old Christine (8 pm/ET CBS)
Richard and New Christine's wedding day arrives with pranks, tears and quite a few surprises. The laugh-rich Season 4 finale reunites Christine with father-of-the-bride Papa Jeff (Scott Bakula), whom she dumped but is now suddenly hot for again. Romance sparks for Barb, too, with one of Richard's single friends, and Matthew continues his giddy pursuit of the bride's adventurous sister, who is determined to spice up the proceedings with a little naughty fun.
* Criminal Minds (9 pm/ET CBS)
The fourth season comes to a close with two back-to-back episodes that send the agents on a chase that takes them across the U.S. border. It begins in Detroit, where the BAU searches for a serial killer who targets those on the fringe of society. It concludes with the team pursuing the psychopath into Canada, where an agent's life is threatened.
* Blueprint America: Road to the Future (8 pm/ET PBS)
Will the influx of federal stimulus money to the states and localities be used wisely or just used? This timely documentary from former CNN reporter Miles O'Brien explores the nation's present and future infrastructure and transportation needs, and highlights innovative projects that are being considered or developed in Denver, New York City and Portland, Ore.
* Clean House: Search for the Messiest Home in the Country (10 pm/ET Style)
Niecy Nash and her team of clean freaks scoured the nation to find the seven messiest, cluttered and overall disgusting houses in the U.S. for this new limited series. And they found them! Seven homes. Seven states. The brave cleaning crew begins their chores in St. Louis with a family that includes three monkeys who sleep with their owners. Eeewww!