You could try my terrain modeller TOTAL TERRAIN (or TT2) - click my signature. The sculpting functions are smooth as they use sinwaves.
If you want to make them wrap around, what you could do is this: Make your terrain, then use photoshop or something to scroll the heightmap bitmap so the seams are in the middle (ie if it's a 256x256, offset by 128, 128), then load it back into Total Terrain and smooth out the seams.
If you want to make them wrap around, what you could do is this: Make your terrain, then use photoshop or something to scroll the heightmap bitmap so the seams are in the middle (ie if it's a 256x256, offset by 128, 128), then load it back into Total Terrain and smooth out the seams.