We've had similar question few days ago, but there the requirement was that it only reads a part of the file. There are also these windows questions: http://superuser.com/questions/4044/ and http://superuser.com/questions/3474 but I'm looking for program that works on Ubuntu.
My problem is that due to some bug my .xsession-errors started to increase at alarming rate and quickly took up all my remaining disk space (around 37.1GiB), as I explained in http://superuser.com/questions/184830.
less proved to be useful there, but in files of that size, it was very difficult to get the idea what's going on using less. I'm looking for some program (GUI is a plus) which can read files of that size and allow quick scrolling through them or to at least be capable of going to certain position in a file, like for example 25%, 50% etc.