-New York’s Madison Square Garden will host a Katrina benefit, ”The Big Apple to the Big Easy,” on Sept. 20. Elton John, Jimmy Buffett, Rod Stewart, Stevie Nicks, Lenny Kravitz, John Fogerty, Loggins and Messina, Earth, Wind & Fire, the Neville Brothers, and the rescued Fats Domino are among the performers.

John Grisham appears to be the most generous celeb so far; the Mississippi-based author has donated $5 million to relief efforts. Steven Spielberg is donating $1.5 million. The Hollywood Foreign Press Association, the group behind the Golden Globes, gave $250,000.

Kevin Smith is hosting an online auction at his website, with proceeds going to the Red Cross. Among the items up for bidding are a cameo in Clerks 2: The Passion of the Clerks.

-Farm Aid guru Willie Nelson has launched a drive to help farmers hit by Katrina.

-Warped Tour organizer Kevin Lyman plans a fundraiser, ”Unite the United,” on Oct. 8 in Irvine, Calif. Hoobastank, the Used, and Pennywise are among the performers.

Wilco, three of whose members come from Katrina-ravaged areas on the Gulf Coast, is auctioning off autographed posters at the band’s website.

-Following Wil Wheaton‘s lead, will host a celebrity poker tournament Friday, with the $100,000 pot going to the Red Cross. Participants include poker champ Jennifer Tilly, pop-rock couple Hilary Duff and Joel Madden, Hank Azaria, Shannon Elizabeth, Ron Livingston, Danny Masterson, and Jeremy Sisto.

-Mississippi-based rapper David Banner, who’s been sharply critical of the federal response, is hosting a benefit on Sept. 17 in Atlanta, with Nelly, Twista, and Young Jeezy on the bill. Proceeds go to Katrina relief via Banner’s Heal the Hood foundation.

Timbaland, who said he plans to donate goods when he visits shelters in Texas this week, urged the hip-hop community to stop spending money on bling and start spending it on necessities for the displaced.

Moby, Tim Robbins, John Cusack, and Rosie Perez are among the stars who have recorded public service announcements on behalf of, urging people to offer shelter to Katrina evacuees.

-In other Katrina news: ABC is going ahead with Invasion as scheduled on Sept. 21. It started airing promos again yesterday, but hurricane scenes in the pilot have been toned down.

-Katrina dominates the Nielsen ratings: NBC’s Wednesday edition of Dateline is last week’s top-rated show (12.2 million viewers), with three other primetime Katrina news broadcasts in the top 10. Nielsen didn’t rate Friday’s commercial-free telethon on NBC/MSNBC/CNBC, but the network claims that 13.8 million watched at least some of the show on the three channels.