MacBook Pro to external 24" HP Compaq at 1920x1200 using Mini DisplayPort to VGA adapter I just upgraded OS X from 10.7 to 10.8.
While using 10.7 with an HP Compaq LA2405wg external monitor connected via Mini DisplayPort to VGA adapter, I was unable to set this monitor's native resolution of 1920x1200, because it was not listed in OS X's System Preferences &gt; Displays.
After scouring forums and SE sites, I found the application SwitchResX. With this application I was able to install a custom resolution, and then I was able to use this external display at 1920x1200 without issue for almost a year until I upgraded OS X.
After upgrading to 10.8, my custom resolution was lost. Again, the 1920x1200 resolution is not listed in OS X's System Preferences &gt; Displays. The highest resolution I can use (with correct ratio) is now 1440x900, which is the same as the LCD screen on the MBP.
So I fired up SwitchResX to re-install the resolution, but I am now being nagged about my trial time expiring. When I select my display on the left hand side of SwitchResX, and open the Custom Resolutions tab, I see my resolution listed, but it always says Not installed under the Status column.
Since this exact same hardware configuration worked under 10.7 (with the help of non-free third-party software), it seems like I should be able to get 1920x1200 from 10.8 as well. The only software workaround I knew (SwitchResX) has expired.
Is there anything I can do with OS X to reclaim my monitor's native resolution? Or do I really have to resort to purchasing third-party software to support this seemingly common resolution?

System specs:
OS X 10.8.4, Intel Core i7, 4GB DDR3 RAM, AMD Radeon HD 6490M 256MB

Edit - Bounty Details:
I have Apple's Mini DisplayPort to VGA adapter. Their knowledge base entry about supported resolutions and refresh rates here:
http://support.apple.com/kb/ht3382#16
And the native resolution and refresh rate for my monitor is 1920x1200 @ 60Hz. You can view the manufacturer's product page here:
http://h20000.www2.hp.com/bizsupport/TechSupport/DocumentIndex.jsp?lang=en&amp;cc=us&amp;contentType=SupportManual&amp;prodTypeId=382087&amp;prodSeriesId=3955381
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http://www.fieggen.com/shoelace/shoelaces.php
I've had the same problems. 

I think youre leaving the lid to your mac open.

If you are using an external keyboard, external mouse, and an external display, while your mac is powered, you can close the lid, hit the shift key a couple times to wake it up and I think you will see the desired resolution listed. 

There is a command line solution

Get this

After you compile it by running:

./configure

make

sudo make install


you can do 

$ screenresolution get
Display 0: 1280x800x32
$ screenresolution list
Available Modes on Display 0
  1280x800x8    1280x800x16     1280x800x32     1280x800x30 
  1152x720x8    1152x720x16     1152x720x32     1152x720x30 
  1024x768x8    1024x768x16     1024x768x32     1024x768x30 
  1024x768x8    1024x768x16     1024x768x32     1024x768x30 
  1024x640x8    1024x640x16     1024x640x32     1024x640x30 
  800x600x8     800x600x16  800x600x32  800x600x30 
  800x600x8     800x600x16  800x600x32  800x600x30 
  800x500x8     800x500x16  800x500x32  800x500x30 
  640x480x8     640x480x16  640x480x32  640x480x30 
  640x480x8     640x480x16  640x480x32  640x480x30 
  720x480x8     720x480x16  720x480x32  720x480x30 
  720x480x8     720x480x16  720x480x32  720x480x30 

$ screenresolution set 1280x800x32
Setting mode on display 0 to 1280x800x32