If you need to script out a list of available site templates, here is the answer.

Add-PSSnapin Microsoft.SharePoint.PowerShell –erroraction SilentlyContinue
$site = Get-SPSite "http://www.sharepointed.com/tacoSiteCollection"
$web = $site.RootWeb
$listTemplates = $site.GetCustomListTemplates($web)

foreach($xx in $listTemplates)
 {
 Write-Host $xx.FeatureId
 }

$site.Dispose()

How do you create a calculated column using PowerShell?  In my example, I’m creating a new field called Calculated Date Field, setting the formula, then setting the output type to DateTime.

How do I build the formula?  Go into your list, add a new calculated column, create your formula, test the formula.  If it works, copy the formula and delete the column.

$site = Get-SPweb "http://sharepointed.com/site/salsa/"

$mList=$site.Lists["Nacho"]

 $mList.Fields.Add("Calculated Date Field", "Calculated", 0)
 $SPField = $mList.Fields.GetField("Calculated Date Field")
 $SPField.Formula="=DATE(YEAR([Document Date])+7,MONTH([Document Date])+0,DAY([Document Date])+0)"
 $SPField.OutputType="DateTime"
 $SPField.Update()

$site.Dispose()

If you are looking for a way to get all of the subsites for a given site, PowerShell can help.

Add-PSSnapin Microsoft.SharePoint.PowerShell –erroraction SilentlyContinue

$spWeb = Get-SPweb "http://sharepointed.com/sites/taco"

	foreach($subSite in $spWeb.Webs)
		{
			$subSite.Title
			$subSite.Dispose()
		}

$spWeb.Dispose()

1. add the SharePoint Snapin
2. get the site that we want to dig into.
3. loop on each subsite
3.1. display the site title
3.2. close the connection to the subsite.
4. close the connection to the site we dug into.

Get-SPWeb : Cannot access the local farm. Verify that the local farm is properly configured, currently available, an
d that you have the appropriate permissions to access the database before trying again.

I was using one of the farm service accounts to run my PowerShell scripts, not good.
The service account was locked and caused the above error.

Here is the error:
The following exception was thrown when trying to enumerate the collection: “One or more field types are not installed properly. Go to the list settings page to delete these fields.”.
At C:\Users\me\AppData\Local\Temp\2\bca6fde0-a91f-427a-ad21-4794d47cebfc.ps1:24 char:17
+ $spList.GetItems <<<< ($spQuery)
+ CategoryInfo : NotSpecified: (:) [], ExtendedTypeSystemException
+ FullyQualifiedErrorId : ExceptionInGetEnumerator

Why?
Using PowerShell, I was trying to query a list. In my Where statement, I was calling a field by its display name, and not its INTERNAL name.

Bad code:

$web = Get-SPWeb "http://sharepointed.com/sites/taco"

$spList = $web.Lists["Taco History"]
$field = $spList.Fields["Taco Name"]
$value = "Grande Taco"

# Create Query based on field and value
$camlQuery =
'' +
$value +
'';
# SPQuery object
$spQuery = New-Object Microsoft.SharePoint.SPQuery
# Add query
$spQuery.Query = $camlQuery;
$spList.GetItems($spQuery)

This code will toss you the One or more field types are not installed properly….. error.

Using the friendly U2U Caml query tool, I rewrote my PowerShell Caml query. Doing this I noticed my field name issue. My fields display name is Taco Name but its internal name is Taco_x0020_Name. Doh!!!

Rewrite the PowerShell script and life is good!
Notice the new $field = $field.InternalName line in the script.

$web = Get-SPWeb "http://sharepointed.com/sites/taco"

$spList = $web.Lists["Taco History"]
$field = $spList.Fields["Taco Name"]
$field = $field.InternalName
$value = "Grande Taco"

# Create Query based on field and value
$camlQuery =
'' +
$value +
'';
# SPQuery object
$spQuery = New-Object Microsoft.SharePoint.SPQuery
# Add query
$spQuery.Query = $camlQuery;
$spList.GetItems($spQuery)