I've seen a lot of jigs to do edge jointing on a table saw or router, including this question. I haven't seen much for flattening one of the faces, though. If the board is narrow (less than ~3"), I can run it on the freshly-jointed edge through my table saw and flatten and square the face that way. But what about wider boards? Hand planes would work, of course, but are there other methods using a table saw, router, and/or jigs like there are for edge jointing?
Possibly the best method to flatten the face of a board using power tools not specifically designed for that job is with a router mounted in a planing sled/levelling sled. There are abundant versions of this posted online so this is just a sample:
It must be said though, this technique is perhaps best kept in reserve for major stock removal, e.g. taking out most or all of the bow or twist from particularly hard or gnarly woods, flattening wide boards or glue-ups and for slabs, not used for everyday flattening of stock. It can however be considered the go-to method for flattening the tops of stumps or trunk slices, and for conventional butcher blocks, where you're dealing with all end grain which is punishing to plane manually and dangerous to run through a thickness planer.
If you want to see these in action here are a few YouTube links:
Joint and Thickness-Plane with a Router from American Woodworker
Flattening Boards with a Router Sled from Matt Cremona
174 - Flattening Workbenches and Wide Boards With A Router from The Wood Whisperer
There are jigs which are used for flattening the face of large slabs, which are basically a rail on each side with a rigid beam bridging them to carry a router. As far as I know, the folks who use these follow up with jointer planes and winding sticks to make sure the surface is really flat without dips or twist.
If you have a planer, a jointing sled on the planer might be a suction. If you have a large drum sander, a simar sled on that might be worth trying.
Depending on the size of the job and what you are starting with, going straight to a traditional jointer plane might be just as fast as any of the powered solutions.
Two additional methods using a planer.
The first is to make a jig consisting of a flat length of ply or mdf. Put the wood to be jointed on top, and use a series of wedges to "level" the bottom of the board and stop it rocking. (Double sided tape helps to keep them in place. Once ready you can pass the board through the planer as normal to make side level, then flip and level the other side. Picture below for clarity - but if you're going to try this I would recommend watching one of the many youtube videos demonstrating it.
Handplane and Planer
The other option is to use a handplane to roughly level the board. Contrary to popular opinion, a board doesn't have to be 100% perfectly jointed to run through a planer - particularly if it's thick or short.
You can use a hand plane to roughly level the board, making sure it sits roughly flat and fairly stable (ie doesn't rock). Once this is done, you can pass this through a planer, roughly flattened side down. When the top is planned flat and smooth, then flip again to level the other side.
This has worked well for me for wood up to about 3' or 4' in length. If I had need to flatten something longer I would probably try the sled method above.
I mill a fair chunk of my own lumber - often this leaves me with wood less than 3' long, but about 2" - 3" thick. Provided the milling left a reasonable surface I'll run it through the planer as is. The wood is too thick and short to banana in the planer. The main thing to watch out for here is that the board is hitting the planer relatively level. If the bottom of the board is curved, the curve itself will lift up the board as it goes through, resulting in a non-flat bit of wood.