More detail about what you've been doing and how you've been eating leading up to this plateau would give us a better idea of what might need attention. Really not much info to go on so far. If you're trying to get lean and build strength, it could be something as simple as having your daily calories too low.
What's your current general bodyfat? What are your current maxes on the basic lifts? To clarify, what exactly do you mean by "plateau" anyway, like you haven't seen strength increases in a while? How long have you been stalled? And, again, what's your diet like?
There are tons of programs on here that could be worth trying for a while, but I'm not sure if you're looking for a full program or a "core workout" like just for abs.