Rumor had it that a GPS guided round was being developed for artillery.
I'm assuming it would be able to be modified for tanks as well.
Down to 81/82mm for mortars now too, per the British terminally-guided Merlin 81mm mortar round for their L16 81mm- AKA the U.S. M252. Mortars have such a lovely incoming trajectory for use with self-forging antitank penetrator weapons....
And the US Army has the XM395 laser-guided 120mm mortar round almost ready for fielding in FY 2006. 
Mortars are great for just about any target if you put a smart head (or cluster of smart independently targeted heads) on them. They are also nice and portable.
The US military has been investing a ton of money in advanced mortar systems. Not only are they building new mortar platforms out of composite materials (the new versions of the classic mortars weigh half as much as the ones they replace), but they are making them very smart guided munitions by default, with smart self-homing (i.e. no target designation required -- the warhead searches for a target on the way down) under late-stage development.
This is part of the reason that artillery is getting cut. The US military has decided to put its money in substantially upgrading the lethality and capabilities of the mortar systems for indirect fire missions, in part because it is cheap and very portable, and then leaving the long-range and heavy targets to the Air Force. It is an issue of maximizing bang for the logistical buck. One can make arguments against this, but this is the calculus that was used.