Aside from the 24-105 are there any y other decent value zooms for the 6D?
When you say "decent value" I take it you mean "cheap"?
To which, in all honesty, the answer is really "no".
There are some cheaper Canon zooms that will fit, but they are old designs, dating from the days of film, and are not ideal to use on FF digital.
The only one that looks worth considering is the EF 28-135mm f/3.5-5.6 IS USM.
It's an old design (1998) and was one of the first Canon lenses with IS.
There's a review of it here
http://www.photozone.de/reviews/190-canon-ef-28-135mm-f35-56-usm-is-test-report--review
Without wishing to sound snobbish, but with the IQ available from the 6D I wouldn't put any zoom on it that didn't have a red ring around the end.
I know it's not cheap, but the 6D kit with the included 24-105 is very good value.
I was a bit sceptical about the 24-105 myself, since it's not the most modern design, but since I bought it I find I really like it. Sure there is some distortion at the 24mm end, but if you use Lightroom or DPP you can remove the distortion in software.
I'm extremely happy with mine, although like all things Canon, it is possible get a poor example.
I also have the 17-40 F4L and the 70-200 F4L which I previously used with my crop body 30D.
With the crop body I never noticed any problem, but with the FF I needed something to cover the gap between 40 & 70mm, hence buying the 24-105 kit.
One additional benefit is that the same sized filters will fit all the lenses.