***some serious spoilers for the next few weeks....***General Spoilers:
5/20/08 (Tu.) 8:00 PM CBS (#518/519) **finale/2 parter**
5/13/08 (Tu.) 8:00 PM CBS (#517)
5/6/08 (Tu.) 8:00 PM CBS (#516) Recoil
4/29/08 (Tu.) 8:00 PM CBS (#515) In The Zone
4/22/08 (Tu.) 8:00 PM CBS (#514) Internal Affairs
4/15/08 (Tu.) 8:00 PM CBS (#513) Dog Tags
4/8/08 (Tu.) 8:00 PM CBS (#512) Stakeout
The exiting NCIS series regular will be tragically murdered in one of this season's five remaining episodes. Source: Ask Ausiello @ TV Guide
Sources confirm that a major castmember - a series regular - is on the way out. [...] The actor in question will exit the series in a dramatic fashion. I might even go so far as to call it a major freakin' twist, the repercussions of which will be felt well into next season and, perhaps, beyond. One thing I feel reasonably comfortable letting you know is that the aforementioned twist does, in fact, occur this season - i.e., sometime between tomorrow night's post-strike return and the season finale in May.
Source: The Ausiello Report [Note: In another article, Ausiello confirms that by series regular he means one of the following: Mark Harmon, Pauley Perrette, Cote de Pablo, Lauren Holly, Michael Weatherly, David McCallum and Sean Murray.]
"We've had flashbacks to a relationship that Jenny and Gibbs had in Paris while they were working undercover," says executive producer Shane Brennan. "Now the secret past will come back to haunt them, leading to an emotionally devastating two-hour season finale." Source: TV Guide
Medical examiner Ducky drops a bombshell that causes tension between Gibbs and Director Jenny Shepard.
The flirty relationship between Tony and Ziva is derailed when he runs off to Baghdad with returning intel analyst/germaphobe Nikki Jardine (Susan Kelechi Watson). Source: Entertainment Weekly

credit to:DiNozzo Devotee