This is the home of both the post-CSI timeslot and the post-Grey's timeslot. There's been a lot of activity.
ABC: The first lead-out for Grey's Anatomy on Thursday was JJ Abrams offering Six Degrees but it really struggled and eventually saw Friday/ABC.com duty. It was replaced by a somewhat promising Friday show called Men in Trees which had at least marginal improvements in retention and got another season (but back to Friday). Late in '06-'07 the net debuted some other series, like six episodes of October Road and tryouts for Notes from the Underbelly and Traveler. For fall '07 it was the "male Desperate Housewives," Big Shots, and while it did pretty poorly it played out its entire 13-ep order in large part because the writer's strike hampered the available options. During the strike ABC moved Lost into a Thursday anchor spot and its lead-out was legal newbie Eli Stone. When Grey's came back post-strike Lost got bumped up into this 10:00 hour. For fall '08 it was another newbie in '70s cop drama Life on Mars, but it eventually got moved to Wednesday for a post-Lost tryout while fading Grey's spinoff Private Practice came over to the post-Grey's spot for a boost. No doubt it got one and it returns to the slot for '09-'10. Originals in this timeslot averaged a 3.8 demo though that was boosted by some crossover episodes. Most eps fell between 3.3 and 3.6.
CBS: One of the most iconic three-hour blocks of TV in recent memory was CBS' Survivor/CSI/Without a Trace Thursdays. But in fall of 2006 CBS finally elected to break it up, sending Trace to prop up Sunday and bringing in legal newbie Shark. Shark had OK retention and got renewed, but it was Sunday-bound this time while WAT returned to solidify Thursday again. However, a year of disappointing retention saw it moved again for fall 2008, this time to Tuesdays at 10 to prop up a historically rough timeslot for the eye. Newbie Eleventh Hour took over for most of the season, then horror dud Harper's Island and crime repeats saw some late-season action . CBS will continue to alternate between known quantities and newbies, this time bringing over last year's breakout hit The Mentalist in a move many see as a precursor to Mentalist taking over at 9. It has almost without fail built out of CSI in reruns this summer, a good omen for fall '09.
NBC: This is, of course, the very long-time home of medical drama ER, and it's aired in the timeslot each of the last three years. However, there have been some fill-ins recently, first newbie Lipstick Jungle during the '08 writer's strike, then new cop drama Southland at the end of '08-'09 after ER finally aired its series finale. This year, it's The Jay Leno Show taking over here just like every weeknight at 10.
Cable Notables: FX has had a comedy foothold in this timeslot thanks to veteran It's Always Sunny in Philadelphia, and it's joined by newbie Archer this fall.