What are the advantages of Python, PowerShell, and other scripting environments?  We would like to standardize our scripting and are currently using bat and cmd files as the standard.  I think Python would be a better option than these, but am also researching PowerShell and other scripting tools.
The scripts would be used to trigger processes such as wget etc to call web services, or other applications/tools that need to run in a specific order with specific parameters.
We primarily work with the Windows stack, but there is a good chance we will need to support Unix in the future.
Python works as a great, all-purpose tool if you're looking to replace CMD and BAT scripts on your Windows boxes, and can also be written to run scripts on your (L)inux boxes, too. It's a great, flexible language and can handle many tasks you throw at it.
That being said, PowerShell is an amazingly versatile tool for administering all manner of Windows boxes; it has all the power of .NET, with many more interfaces into MS products such as Exchange and Active Directory, which are a timesaver. Depending on your situation, you may get more use of of PS than other scripting languages just because of the interfaces available to MS products, and I know MS seems to have made a commitment to providing those APIs in a lot of products. PowerShell comes installed on all current versions of Windows (Windows 7+, Windows Server 2008+), and is fairly easily installed on older versions.
To address your edit that your scripts will be used to launch other processes, I think in that case either of the tools fit the bill. I would recommend PS if you plan on adding any admin-ish tasks to the scripts rather than just service calls, but if you stick to what you described, Python is good.
Python, PowerShell, or Other?