There are **many** compactifications of particular groups.
For your example of $\mathbb Z^2$: one construction for a compactification is to first embed it as a subgroup of
$S^1 = \mathbb R / \mathbb Z$ by picking two rationally independent numbers for the images of the generators.
Now compactify $\mathbb Z^2$ by making large elements connverge toward their image points in $S^1$.
The stabilizer of any point is trivial.

The same method works to get a compactification associated with any action of $G$ on a compact space $X$. Just pick a point $x \in X$, and adjoin the closure of the orbit of $X$ at infinity in $G$. If the action has no fixed points in the cloure of the orbit, then stabilizers are trivial. It's easier to avoid all but cyclic stabilizers. To make actions with small stabilizers, you can take products of examples; point stabilizes in the product become intersections of stabilizers in the factors. There are many tricks, some of them useful, for making compactifications that are Hausdorff metric spaces.

There's an ultimate (but non-constructive and of large cardinality) compactification, the Stone-Cech compactification, which has trivial point stabilizers for any group,

Metric spaces of non-positive curvatureby Bridson and Haefliger for details. – HJRW Sep 22 '10 at 15:44notan invariant of the group $G$, so my previous comment was, strictly speaking, slightly inaccurate. But it is well defined for the space $X$, which I think is what you wanted. – HJRW Sep 22 '10 at 15:48