1) Kuwait would not exist (1991).
2) Uday and Qusay would have taken over for their father.
3) Saddam would be retired at Dora Farms.
4) Zarqawi would be on Uday's payroll.
5) Sanctions on Saddam would have ended
6) Saddam would have WMD by now and be working in a nuke, so we'd have 3 rogue states with a nuclear weapon or working on one
7) Saddam would have further boosted Al Qaeda and provided them with logistical and safe haven support more than he had before his overthrow
8) Saddam would have used terrorists to attack the US mainland again as Vladimir Putin warned us in November 2002 that Saddam was planning to do according to their significant intelligence assets in Saddam's Iraq.
I'm sure we could think of several other negative consequences of having left Saddam in power.