There are so many third-party tools to convert from the virtualbox virtual harddisk to .vmdk(in Vmware) or VHD (in Hyper-V), such as Vmware Standalone Converter, Starwind V-2-V tools. But, you can easily use the built-in virtualbox manager to convert from one disk type to another.
Moreover, I found it is much faster than using Vmware standalone converter.
I show the steps are as below: Note that the same procedure should work in linux environment.
2) VBoxManage.exe clonehd c:DiskVirtualold-disk.vdi c:DiskVirtualnew-disk.vmdk –format vmdk –type normal –variant standard
3) Now, you can attach the converted vdisk to the VM of your choice ;P
Sample screenshots as follows: