From Cardy's article http://arxiv.org/abs/cond-mat/0503313
Some important special cases are therefore:
$\kappa = 2$: loop-erased random walks (proven in [24]);
$\kappa = 8/3$: self-avoiding walks, as already suggested by the restriction property, Sec. 3.5.2;
unproven, but see [22] for many consequences;
$\kappa = 3$: cluster boundaries in the Ising model, however as yet unproven;
$\kappa = 4$: BCSOS model of roughening transition (equivalent to the 4-state Potts
model and the double dimer model), as yet unproven; also certain level lines of a
gaussian random field and the ‘harmonic explorer’ (proven in [23]); also believed to
be dual to the Kosterlitz-Thouless transition in the XY model;
$\kappa = 6$: cluster boundaries in percolation (proven in [7]);
$\kappa = 8$: dense phase of self-avoiding walks; boundaries of uniform spanning trees
(proven in [24]).
It should be noted that no lattice candidates for κ > 8, or for the dual values κ < 2, have
been proposed.