Infinite line charge (lambda): Cylindrical Gaussian surface of radius r, length L. Flux = E(2pirL). Enclosed charge = lambdaL. Result: E = lambda/(2piepsilon_0*r).

Infinite plane sheet (sigma): Pillbox Gaussian surface. Flux = 2EA (both flat faces). Enclosed charge = sigmaA. Result: E = sigma/(2epsilon_0).

Two parallel infinite sheets: Same sigma: E = sigma/epsilon_0 outside both sides, E = 0 between them. Opposite sigma (+sigma and -sigma): E = sigma/epsilon_0 between them, E = 0 outside. This is the basis of a parallel plate capacitor's uniform field.

Infinite uniformly charged cylinder (rho, radius R): Inside (r < R): E = rhor/(2epsilon_0). Outside (r > R): E = lambda/(2piepsilon_0r) where lambda = rhopi*R^2.