Modern Mechanized Bridging...

The K-21 post and how that vehicle will conduct river crossing brought up the issue with bridging ops.  I never liked that term because I always considered river crossings as being "inland amphibious assaults".  None the less below you'll see the product offerings from General Dynamics Europe which covers most forms of bridging options for mechanized forces....You can check out there website here.

Beaver AVLB.
I list this system first because it was the standard that replaced the old scissor bridge.  You will find a great many forces world wide still using it but its mostly designed to accommodate heavy mech forces...meaning tanks...which also means that its fallen out of favor, just as tanks are seeing declining use.  Clicking on the name of the system will lead you to the Canadian Army's website where you can find stats of this vehicle.  Note that I did not include the REBS Rapidly Emplaced Bridge System simply because I view that as being the same just scaled for wheeled infantry fighting vehicles.

Improved Ribbon Bridge.
The IRB has been in service for many years with the US Army, Marine Corps and German Army (I've never seen one deployed though).  It can easily handle (according to the manufacturer) most heavy military equipment and because of its width even oversized loads.  You want to bridge the Mississippi?  This is how you do it in combat.

M3.
This is the ultimate bridging vehicle in my opinion.  The M3 can be used as a bridge, as a vehicle lorry and can keep up with mechanized formations without compromising one of your fighting vehicles or taking a MTVR or PLS truck out of action to tow it.

All in all I see bridging ops as a tremendous achilles heel and another reason for all IFVs to be amphibious.  Rivers are natural choke points and that means they're danger areas.

You show me a river and I can dope out likely crossing points.  Of all these systems only the M3 can really help you maintain momentum...even with your tanks.  Its still going to be a tricky operation but ferrying a tank or two (depending on how many of those things you have) across a large inland water obstacle is perferrable to having to cover your combat engineers while they set up your ribbon bridge or assemble a couple of AVLBs to cover the distance.