Is there a tool that can be used to partition a disk (SD card in particular) from the command line? The purpose of this is for batch processing and customized GUI.
I doubt it will work on an SD card, but here is the command: diskpart
KCotreau is right. You can use DiskPart, which is more powerful as a graphical disk management tool.
But there is a problem for some USB sticks and SD cards: They usually don't have a Master Boot Record (MBR).
In such case you have to delete the existing partition and create a MBR. After this, you can create more than one partitions. But sometimes you have to assign drive letter manually, because Windows recognizes just the first partition.
BTW: A advantage of an existing MBR is, that you can boot from such a media.