You should definitely go and read Ezra Klein's handy guide to the various public option compromises that are working their way through the Senate. One thing to bear in mind however is that the public option compromises are really being discussed along two dimensions.
One dimension concerns implementation: when and how does the public option come into being? Does the public option come online right away ("right away" in this instance meaning 2013)? Will it come online immediately, but states are allowed the right to opt out of it? Alternatively, might states have to affirmatively opt into the public option? Or might the public option be implemented only by a trigger?
The other dimension concerns the public option's operation. Will it operate as a federal program charging Medicare (or Medicare +5%) rates? As a federal program that must negotiate its rates in the market? As programs run by state governments? Or as non-profit co-ops, operated on a state-by-state basis, but not run by state governments themselves?
If you drew a grid of these issues in two dimensions, then almost every box would be filled by some or another version of the "public option". Actually, let's go ahead and do that...
The yellow triangle represents the sort of "Zone of Compromise". I'm pretty sure that a co-ops provision, with immediate implementation, could pass the Senate (or at least not be filibustered by it). Likewise with Olympia Snowe's trigger. A strong-ish opt-in amendment proposed by Maria Cantwell was approved by the Senate Finance Committee along party lines, but did not get Snowe's vote; it might or might not pass the full Senate.
Basically, any square that is overlapped by the triangle seems like a plausible outcome. The most robust public option available is probably a federally-run program that states would have the right to opt out of and which would have to negotiate its rates in the market. The worst-case scenario is probably state level programs with an extremely stingy trigger, as proposed by Snowe. (This is assuming, of course, that health care reform as a whole will pass, which people may be a little bit too sanguine about.)
This is not a perfect representation of the alternatives by any means. Co-ops and government-run programs are not necessarily mutually exclusive. A "loose" trigger could conceivably be more robust than an opt-in provision, or even an opt-out provision, although in practice Snowe's proposal is not. Moreover, state-level options and triggers could be combined in various ways: maybe states have to opt in initially, but they'd be enrolled automatically if a trigger kicks in. An final complication is is that certain of the options -- for instance, a state-run opt-out -- do not make particularly much sense. Still, it should provide a reasonably useful schematic.
Note: Chuck Schumer's position has been clarified in the chart based on some helpful feedback from his office.