TONIGHT'S MUST-SEE

"It's Always Sunny in Philadelphia," 7:30 p.m., FX. In its own modest, eccentric way this show —about three men and one woman, all self-centered and groping with city life as they run a struggling bar in Philadelphia — is trying to fill the gap left by "Seinfeld." Tonight's episode has a long-ago girlfriend (Heather Donahue of "The Blair Witch Project") announcing that Charlie has a son. Charlie decides the kid can help his dating life. Meanwhile, Mac and Dennis decide an abortion protest will be a great place to pick up chicks. They're a shallow bunch and get what they deserve. "Sunny" lacks the "Seinfeld" genius but does have some fun moments.

OF NOTE

"Big Brother 6," 7 p.m., CBS. It's time for the fifth person to be ousted.

"Joey," 7 p.m., NBC. Christina Ricci shows up as Joey's sister, an aspiring socialite who keeps reminding everyone how rich she is. Meanwhile, Michael doesn't know a hot girl is pursuing him.

"Starved," 7 p.m., FX. If possible, this second episode is even more distasteful and unfunny than the opener. Sam (Eric Schaeffer) loves getting colonics — and loves the woman who administers them.

"Will & Grace," 7:30 p.m., NBC. Jack and Will plan to buy a vacation home in what they think is the currently hot gay neighborhood.

"CSI: Crime Scene Investigation," 8 p.m., CBS. Brass (Paul Guilfoyle) heads to Los Angeles after a friend of his estranged daughter is killed.

"Hooking Up" finale, 8 p.m., ABC. This series has been tracing the dating life of New York City women. In particular it's given attention to Amy, who has demands: The right guy is a morning person; he doesn't play video games, live with his mom or watch sports on a sunny day. Tonight, we'll see how she does.

"ER," 9 p.m., NBC. The Iraqi burn victim has been flown to County General, and Neela is surprised that Gallant has made the trip, too.

"Without a Trace," 9 p.m. CBS. When a woman disappears, a hate crime is suspected.