Hi Matthew - hope you have already figured this out. LevelList is indeed where you want to go. You may also want to set the CLim. Here's an example:
% create some fake data (between 0 and 1) with outliers at 1800
x = abs(peaks);
x(5:6,5:6) = 1800;
x(15:17,15:17) = 1800;
levels = [0:.1:1 800 1700]; % manually specify where to draw contours
contour(x,'LevelList',levels);
set(gca, 'CLim',[0 1.2]); % set CLim to be the range of most of your data