  The existence of a global attractor for wave equations in unbounded domains
is a challenging problem due to the non-compactness of the Sobolev embeddings.
To overcome this difficulty, some authors have worked with weighted Sobolev
spaces which restrict the choice of the initial data. Using the "tail
estimation method" introduced by B. Wang for reaction diffusion equations, we
establish in this paper the existence of a global attractor for two wave
equations in the traditional Hilbert spaces $\displaystyle H^1(\Omega)\times
L^2(\Omega)$ where $\Omega$ is an unbounded domain of $\R^N$. The first
equation, with a mass term is studied in the whole space $\R^N$ and the second
one without mass term is considered in a domain bounded in only one direction
so that Poincar\'e inequality will hold.
