The peacock network held its upfront presentation this week and execs presented their new schedules to advertisers. NBC has been having a lot of trouble in the last couple of years so the network has decided to give Jay Leno a new show and air it five nights a week at 10pm. As a result, the network has five fewer primetime hours to fill with other shows.

New shows coming next season include medical series Trauma and Mercy; Day One, a show about a post-catastrophe world; a self-improvement series called Breakthrough with Tony Robbins; a reality-style show from Jerry Seinfeld about marriage called The Marriage Ref; a reality competition for a capella groups called The Sing-Off; a series about celebrity’s family trees titled Who Do You Think You Are?; a Friends-like sitcom called 100 Questions; and a comedy centered around a community college called Community. The new version of Parenthood also made NBC’s schedule.

America’s Got Talent will return this Summer. It’ll be joined by new shows like The Great American Road Trip, I’m a Celebrity… Get Me Out of Here!, The Listener, Merlin, and The Philanthropist.

Shows that will be back next season include 30 Rock, Celebrity Apprentice, The Biggest Loser, Chuck, Dateline, Friday Night Lights, Heroes, Law & Order, Law & Order: Special Victims Unit, The Office, Parks and Recreation, Southland, and Sunday Night Football.

Which NBC show shouldn't have been cancelled? America's Toughest Jobs The Baby Borrowers Celebrity Circus Celebrity Family Feud The Chopping Block Crusoe Deal or No Deal ER Fear Itself Howie Do It Kath & Kim Kings Knight Rider Last Comic Standing Life Lipstick Jungle Medium Momma's Boys My Name Is Earl Most Outrageous Moments My Own Worst Enemy Nashville Star Superstars of Dance View Results  Loading ...

Can’t find your favorite NBC show among those lists? Well, here are more than two dozen that won’t be back next season…

America’s Toughest Jobs
A reality show in which contestants try difficult and dangerous occupations. The winner takes home the combined first year salaries of all of the sampled jobs. The series performed poorly in season one and was shuffled to Saturday nights for its final installments.

The Baby Borrowers
Based on a UK series of the same name, five young couples get a feel for what it’s like to take care of a baby for three days, then a toddler, a pre-teen, a teenager, and an elderly person. The network took a lot of flack for “borrowing” infants and didn’t even get good ratings.

Celebrity Circus
Pop culture stars are trained in circus acts and then perform for judges and home viewers to stay in the competition. Antonio Sabato, Jr. won the first season’s competition but there won’t be a second year.

Celebrity Family Feud
Al Roker (The Today Show) hosts the newest version of the classic TV game show with celebrity families competing for cash prizes that are given to charity. Six episodes were produced and aired but not enough people watched.

The Chopping Block
The Chef Ramsay-like reality show was pulled after three installments and terrible ratings. The network immediately began airing the remaining episodes online but will it back on Friday nights in mid-June.

Crusoe
Based on the classic Robinson Crusoe novel, this series never achieved good ratings and was stranded on Saturday nights. All 13 episodes aired.

Deal or No Deal
The game show was a great success initially but then the network overexposed it. Audiences became tired of it and ratings dropped off. After four years and 197 episodes, NBC has cancelled the game show. The syndicated version will continue to appear in daytime.

ER
The venerable NBC medical drama that follows doctors and patients at a Chicago hospital. The show lasted 15 seasons and lots of changes is castmembers.

Fear Itself
This series is an anthology of horror/suspense stories, directed by well-known directors like Stuart Gordon, Brad Anderson, John Landis, and Rob Schmidt. Unfortunately, the series couldn’t scare up many viewers and NBC only aired eight of the 13 produced installments.

Howie Do It
A practical jokes series, led by Howie Mandel, that lasted just a single season of 20 installments. The ratings didn’t make the network smile.

Kath & Kim
A remake of an Australian series, this sitcom revolves around a dysfunctional mother and daughter relationship. Low viewership doomed this series to a 17 episode run.

Kings
NBC had great expectations for this grandiose drama but it didn’t catch on. The final episodes will begin airing on Friday nights next month.

Knight Rider (2008)
This continuation of the 1982 David Hasselhoff series didn’t take off with enough viewers and has been cancelled after a shortened season of 17 episodes.

Last Comic Standing
A reality show competition that seeks to find the most talented stand-up comedian. The winner receives his own comedy special and a development deal with NBC. Created by Peter Engel (Saved by the Bell), Standing has been hosted by Jay Mohr, Anthony Clark, Bill Bellamy, and Fearne Cotton. The series ran for six seasons and 59 episodes.

Late Night with Conan O’Brien
The late-night talk show host is moving to the West Coast to take over The Tonight Show. O’Brien began as a veritable unknown but the show ran for 2,725 episodes and 16 seasons.

Life
The ongoing story of Detective Charlie Crew lasted just two seasons and 32 episodes. The ratings weren’t high enough for a third season, even for the struggling peacock network.

Lipstick Jungle
The series about three powerful and beautiful ladies from the big apple, lasted just two short seasons and 20 installments.

Medium
Though the show was still a decent performer for the peacock network, NBC cancelled the Patricia Arquette series after five seasons. Fortunately, CBS picked it up and will run season six on Friday nights.

Momma’s Boys
Co-executive produced by Ryan Seacrest (American Idol), this reality show centers around a group of mothers who help to choose a mate for their complacent sons. All six episodes of season one aired and there won’t be any more.

My Name Is Earl
NBC has cancelled the Jason Lee comedy about karma correction after four seasons. The show is currently being shopped to other networks and may end up on FOX.

Most Outrageous Moments
Used mostly as filler by the network, this series showcases humorous clips from television and everyday situations. A few unaired episodes will pop up in the coming months (July 21st, July 28th, August 26th, and August 28th) but no other original episodes will be produced.

My Own Worst Enemy
Christian Slater’s foray into series television was cut short after only nine episodes. Viewers were left hanging and were robbed of any resolution.

Nashville Star
A reality competition that ran for five seasons on USA Network before moving to NBC. Billy Ray Cyrus hosted the most recent run, season six. The show’s been cancelled by the peacock network and there’s been no mention of the series returning to its original cable home.

Superstars of Dance
A dance competition series that pits groups of eight international dancers against one another. Hosted by Riverdance veteran Michael Flatley, this show lasted five episodes. It won’t be coming back for season two.

The Tonight Show with Jay Leno
After 17 years, the late night talk show host turns over the venerable program to Conan O’Brien. Leno will be moving to his own primetime series in September 2009.

Will you miss any of these cancelled shows? Has NBC made any mistakes or have they gotten these right? See any they shouldn’t have renewed but did? Leave your comments below!

Images courtesy NBC.