The medians $AD$, $BE$, and $CF$ of triangle $ABC$ intersect at the centroid $G$.  The line through $G$ that is parallel to $BC$ intersects $AB$ and $AC$ at $M$ and $N$, respectively.  If the area of triangle $ABC$ is 810, then find the area of triangle $AMN$.
We know that $AG:AD = 2:3$.  Triangles $AMG$ and $ABD$ are similar, so $AM:AB = AG:AD = 2:3$.  Likewise, $AN:AC = AG:AD = 2:3$.

[asy]
import geometry;

unitsize(1 cm);

pair A, B, C, D, E, F, G, M, N;

A = (1,3);
B = (0,0);
C = (4,0);
D = (B + C)/2;
E = (C + A)/2;
F = (A + B)/2;
G = (A + B + C)/3;
M = extension(G, G + B - C, A, B);
N = extension(G, G + B - C, A, C);

draw(A--B--C--cycle);
draw(A--D);
draw(B--E);
draw(C--F);
draw(M--N);

label("$A$", A, dir(90));
label("$B$", B, SW);
label("$C$", C, SE);
label("$D$", D, S);
label("$E$", E, NE);
label("$F$", F, NW);
label("$G$", G, SSW);
label("$M$", M, NW);
label("$N$", N, NE);
[/asy]

Therefore, the area of triangle $AMN$ is $810 \cdot (2/3)^2 = \boxed{360}$.