I'd be surprised if there are more than 12 classes released before the end of 2008. That means PHB / DDI / FRCS (?) / Martial Power. You could see some combination of DDI and FRCS / Martial Power, of course, if WOTC "previews" a class using DDI and then officially releases it later.
Here are the classes we know (or are very certain about) already in the PHB:
Cleric
Fighter
Paladin
Ranger
Rogue
Warlock
Warlord
Wizard
In addition, we hear that Barbarian, Bard, and Druid (an possibly Sorcerer) are close to being ready. I guess throw the Swordmage into the fray, though I have seen NOTHING about this Swordmage class other than that it will be in the FRCS or some FR setting book.
It sounds to me like WOTC could do a limited web release of the first two "primal" classes, being the Barbarian and Druid, without doing a "primal" book. We know that Martial Power is the first "power source" book and that there isn't likely going to be another one for a while (2009). I don't see why WOTC would hold off on releasing Barbarian and Druid if they are truly that close to being ready.
Can anyone add anything else to the above?