We provide sharp bounds for the numerical radius of bounded linear operators defined on a complex Hilbert space. We also provide sharp bounds for the numerical radius of AαXB1-α, AαXBα and the Heinz means of operators, where A, B, X are bounded linear operators with A,B≥0 and 0≤α≤1. Further, we study the A-numerical radius inequalities for semi-Hilbertian space operators. We prove that wA(T)≤1-12n-11/n‖T‖A when ATn=0 for some least positive integer n. Some equalities for the A-numerical radius inequalities are also studied.