Question: According to Wikipedia

<http://en.wikipedia.org/wiki/Unix_directory_structure>

<http://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard>

extra disks should not be mounted in `/mnt/` according to the first link, but doesn't seams so according to the second link.

Both say thought that they shouldn't be in `/media`.

**Question**

So where should extra permanent disks be mounted?

Answer: 
According to the FHS link that you gave

```
 /mnt/  Temporarily mounted filesystems.

```

So I assume that you must mean permenantly mounted non-root non-system (meaning not /var/log or similar) filesystems. 

I've always put them in /mnt/fsidentifier and then symlinked to then where needed.

So for instance, I had /mnt/website at one point, /mnt/appdata, /mnt/whatever, then symlink that. I never mounted anything directly to /mnt

If you wanted a "clean" solution, you could write a script to take the UUID of the filesystem, create a mount point for it (under /mnt or wherever you wanted), then mount the filesystem to the mountpoint.
Wherever you like and where it makes the most sense for you. I have seen countless variants. 

Myself, I usually mount them at `/data0`, `/data1` or subdirectories below `/data` and put symlinks to the appropriate places (like `/home`).