I use a home made mini mill.
Full thread in my Mini Mill WIP link in my sig.
Show-off!!! Just buggin' ya, I wish I had the facilities at home to make all the parts for such a rig.
The easiest in-shop edger consists of a known straightedge for a rip fence, such as a jointed 2X6, a couple C-clamps, and a handheld circular saw with a high-quality ripping blade (I use a Freud Diablo thin-kerf). I've edged a number of flitch slabs this way and it works quite well; I can cut almost 3" thick slabs with the 7-1/4" blade and since it's a thin-kerf it hardly slows down at all. Setup can be tedious, but I generally only square one edge of a bunch of pieces, and run them all thru the tablesaw later to square the other edge.
I have seen in-the-field makeshift edgers/ripsaws using chainsaws, one in Malloff's "Chainsaw Lumbermaking" for example, which don't look too complicated. His is only useful as a ripsaw really, as it needs an existing straight edge to guide the board. I guess you could screw a straight board to the edge of an irregular and guide it that way though. Upside to this kind of rig too is that you don't need a big saw, maybe 50cc at most for 2-4" stock.
Having said all that, a Mini-Mill is a great option for edging a whole log before slabbing it. But, flitch-cutting some logs instead of squaring them can result in a significant reduction in waste, so the circular-saw option comes in handy in those situations.