I released DoISO today as GPL open source here: http://opensource.ebswift.com/DoISO/. It is simply a wrapper to mkisofs which is a powerful (but complicated to use) commandline utility. This GUI makes it easy for anyone of any skill level to make an ISO seemingly of any size.
Although it's currently at alpha 1, it works quite well. I'll keep adding properties for all the features of mkisofs so that it will evolve into a fairly sophisticated ISO management program. I have no need for such sophistication, but there's no sense in ignoring all the advanced features of mkisofs.
I made the utility because I couldn't find a free utility which could make a DVD-sized ISO from a filesystem. Someone will probably point out software that I wasn't able to find, but it's too late now, DoISO is gpl'd and at least it exists as an option .
Anyway, I hope some finds this of some use.