I suggest downloading Irfanview (it's free): http://www.irfanview.com/
First of all, you can adjust color balance (shift + U is autolevels, which works usually well enough). Second, you can crop the picture (just use a mouse to choose the area and crop (Ctrl + Y is the shortcut)). Third, you can resize the pic (Ctrl + R). All of these can naturally be found in the menus, too.
Finally, you can combine pics into panoramas.
It won't take long per pic, but the difference is absolutely huge. Highly recommended.