Tomas Restrepo has a nice script for getting/starting/stoping BizTalk Server Applications at: http://www.winterdom.com/weblog/2006/09/02/BTSResetWithPowerShell.aspx

I like how readable it the script is.  It is completely obvious what is going on.  Compare that script with his original C# implementation at:
http://www.winterdom.com/weblog/2005/07/02/BTSReset.aspx

Jeffrey Snover [MSFT]
Windows PowerShell/Aspen Architect
Visit the Windows PowerShell Team blog at:    http://blogs.msdn.com/PowerShell
Visit the Windows PowerShell ScriptCenter at:  http://www.microsoft.com/technet/scriptcenter/hubs/msh.mspx

PSMDTAG:FAQ: How do I start/stop BizTalk Server Applications?

PSMDTAG:TYPE:WMI: MSBTS_HostInstance