The idea of this post is to known someone else's experiences about this subject.
I found very good projects like Lucid Science and it seems to me the best and simplest project designed so far.
http://www.lucidscience.com/pro-vga video generator-1.aspx
Looking for more options, I found kits like this:
The same way, looking on AVRfreaks, there are several "VGA drivers"
It's hard to determinate the relation between time to develop, costs and graphic quality, but if anyone had to take a decision of this kind in the past, or have related experience, i'm glad to read you.