I use an external display for my laptop, windows detected resolution 1280x1024, but Ubuntu config manager detects only 1024x768. I tried to set resolution manually with:
# cvt 1280 1024
# 1280x1024 59.89 Hz (CVT 1.31M4) hsync: 63.67 kHz; pclk: 109.00 MHz
Modeline "1280x1024_60.00" 109.00 1280 1368 1496 1712 1024 1027 1034 1063 -hsync +vsync
# xrandr --newmode "1280x1024" 109.00 1280 1368 1496 1712 1024 1027 1034 1063 -hsync +vsync
# xrandr --addmode VGA1 "1280x1024"
But I have bug with wallpapers: 
With manually set resolution 1600x1280, wallpapers get set correctly, but external monitor cant work with that resolution -_-
p.s. xrandr (VGA1 last two modes that I added manually)
# xrandr
Screen 0: minimum 320 x 200, current 2560 x 1024, maximum 8192 x 8192
LVDS1 connected 1280x800+0+0 (normal left inverted right x axis y axis) 0mm x 0mm
1280x800 59.9*+
1024x768 60.0
800x600 60.3 56.2
640x480 59.9
VGA1 connected 1280x1024+1280+0 (normal left inverted right x axis y axis) 0mm x 0mm
1024x768 60.0
800x600 60.3 56.2
848x480 60.0
640x480 59.9
1280x1024 59.9*
1600x1280_60.00 59.9
