Hi,
You can iterate through all available layouts by means of reflection but for your convenience I post an array containing the currently available layouts:
NLayout[] layouts = new NLayout[] {
new NBalloonTreeLayout(),
new NBarycenterLayout(),
new NCompactDepthTreeLayout(),
new NDockLayout(),
new NFlowLayout(),
new NLayeredGraphLayout(),
new NLayeredTreeLayout(),
new NOrthogonalGraphLayout(),
new NRadialGraphLayout(),
new NSingleCycleLayout(),
new NSpringLayout(),
new NStackLayout(),
new NSymmetricalLayout(),
new NTableLayout(),
new NTipOverTreeLayout()
};