Nelly returns to the top of the Hot 100 for a fourth time, Carrie Underwood notches a pair of country No. 1s and new Billboard charts are among this week's topics.

'GRILLZ' GONE WILD: A surprise 5-1 move carries Nelly to the top of The Billboard Hot 100. "Grillz" (Derrty/Fo' Real) is the fourth No. 1 for Nelly, and the first in two years and four months.

Nelly first topped the chart in June 2002 with "Hot in Herre." That song remained in pole position for seven weeks, and was immediately followed by "Dilemma," which had a 10-week reign. In September 2003, Nelly was back on top with "Shake Ya Tailfeather." Since that hit, Nelly's highest-charting song until now was his collaboration with Tim McGraw on "Over and Over," No. 3 in December 2004.

"Grillz" is the second song to advance to No. 1 in 2006. That's a much faster turnover than last year, when the second song to take over the lead spot was "Candy Shop" by 50 Cent featuring Olivia. That single moved to No. 1 the week of March 4. This is the most rapid succession of No. 1 songs at the beginning of a calendar year since 1991, when Janet Jackson's "Love Will Never Do (Without You)" became the second song to take over the top spot the week of Jan. 19.

BIG 'WHEEL' KEEPS ON TURNING: Carrie Underwood rules Billboard's Top Country Albums chart for the seventh week, while her single "Jesus, Take the Wheel" (Arista) drives 2-1. She is the second "American Idol" contestant to hold sway over this chart. Josh Gracin led the list the week of March 19, 2005 with "Nothin' to Lose."

"Jesus, Take the Wheel" is the 87th No. 1 for the "American Idol" franchise, counting all charts compiled by the Billboard Information Group. The breakdown among the Idols for most No. 1 titles is:

Kelly Clarkson - 32
Fantasia - 11
Ruben Studdard - 10
Clay Aiken - 8
Carrie Underwood - 7
Josh Gracin - 6
Kimberley Locke - 3
Bo Bice - 2
Diana DeGarmo - 1
Tamyra Gray - 1
William Hung - 1
American Idol Finalists - 5

CAST SYSTEM: You don't have to break a leg to be on the newest Billboard chart, but it helps. This week sees the introduction of Top Cast Albums, a tally that measures sales of albums from stage musicals.

Topping the very first chart is "Wicked" (Decca Broadway), the musical that tells the backstory of two Ozzians, the Wicked Witch of the West and her friend Glinda, the Good Witch. The musical opened on Broadway in October 2003 and is still very, um, "Popular."

Another new chart introduced this week is Top Rock Albums. Holding down first place is "First Impressions of Earth" by the Strokes (RCA).

WALKING THE 'WALK': Six weeks ago, Gwen Stefani's "Luxurious" debuted on the Billboard Hot 100. It was the fifth song from her Interscope album "Love. Angel. Music. Baby.' to chart.

Now, Kelly Clarkson's "Walk Away" enters the Hot 100 at No. 97. It's the fifth single from her RCA album "Breakaway" to appear on this list, following the title track, "Since U Been Gone," "Behind These Hazel Eyes" and "Because of You."

A 'FRIEND' IN DEED: A move of 11-8 puts Tim McGraw's "My Old Friend" in the top 10 of Billboard's Hot Country Songs chart for the first time. It is McGraw's 36th top 10 song. Of those 36 hits, 21 have reached No. 1.

TRIPLE PLAY: Three acts have had their first top 10 hits of the 21st century on Billboard's Adult Contemporary chart in the last two weeks.

Hootie and the Blowfish makes a dramatic re-entry at No. 5 with "One Love" (Sneaky Long/Vanguard). The song had been pushed off the list by Christmas music during the holiday season. "One Love" is the first top 10 hit for the group since "Time" clocked in at No. 4 in March 1996.

Eric Clapton is No. 10 on the AC chart with "Say What You Will" (Duck/Reprise). He was last in the AC top 10 in October 1999 with "Blue Eyes Blue."

Melissa Etheridge dips 10-11 with "I Run for Life" (Island). Last week was her first turn in the top 10 since "I'm the Only One" spent two weeks at No. 1 in January 1995.