Best combo I've seen is:
Square, Square, Down+Square, Circle, Up+Square, Square, Square
Not sure on the exact amount of AP, but it's a decent amount.
On a general level, using Down+Square can start off MOST combos with MOST characters. (Sweet Tooth, Kratos and Parappa for sure)
Also from the air:
Air-Forward+Triangle, Foward+Square, Up+Square, Up+Square
Hope this helps.