I have a GOG code I'd like to trade for discounted games (those 1.24$ games), but I'd like to make it a fair trade, so I'm curious which 5.99 games never get discounted?

Arx Fatalis

As Licurg said, Arx Fatalis. The last time it was discounted was December 2012.

This is the ultimate correct answer, lol. :P

If you exclude games that have been released in the past 6 months or so, two $5.99 games have not been discounted in at least the past 18 months:
- Arx Fatalis
- Outcast 1.1

Reference:
[url=http://www.an-ovel.com/cgi-bin/magog.cgi?ver=632&scp=gdspu&dsp=ipgfsorlcmbahT&ord=j0&flt=pie~5.99~psn~1~jnl~31042015~&opt=]http://www.an-ovel.com/cgi-bin/magog.cgi?ver=632&scp=gdspu&dsp=ipgfsorlcmbahT&ord=j0&flt=pie~5.99~psn~1~jnl~31042015~&opt=[/url]

[url=http://www.an-ovel.com/cgi-bin/magog.cgi?ver=632&scp=gdspur&dsp=psrT&ord=C0&flt=pie~5.99~psn~1~&opt=&myf=SatNov142051462015_empty_AFQR7EStEhPzQ]http://www.an-ovel.com/cgi-bin/magog.cgi?ver=632&scp=gdspur&dsp=psrT&ord=C0&flt=pie~5.99~psn~1~&opt=&myf=SatNov142051462015_empty_AFQR7EStEhPzQ[/url]

Here is a link to MaGoG of $5.99 games which have not been on sale since May of 2014...

Thank you guys! :)

Advent Rising goes on sale very rarely