function Export-List([string]$ListURL)
{
[System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint") > $null
[System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint.Deployment") > $null

$versions = [Microsoft.SharePoint.Deployment.SPIncludeVersions]::All

$exportObject = New-Object Microsoft.SharePoint.Deployment.SPExportObject
$exportObject.Type = [Microsoft.SharePoint.Deployment.SPDeploymentObjectType]::List
$exportObject.IncludeDescendants = [Microsoft.SharePoint.Deployment.SPIncludeDescendants]::All

$settings = New-Object Microsoft.SharePoint.Deployment.SPExportSettings

$settings.ExportMethod = [Microsoft.SharePoint.Deployment.SPExportMethodType]::ExportAll
$settings.IncludeVersions = $versions
$settings.IncludeSecurity = [Microsoft.SharePoint.Deployment.SPIncludeSecurity]::All
$settings.OverwriteExistingDataFile = 1
$settings.ExcludeDependencies = $true

$site = new-object Microsoft.SharePoint.SPSite($ListURL)
Write-Host "ListURL", $ListURL

$web = $site.OpenWeb()
$list = $web.GetList($ListURL)

$settings.SiteUrl = $web.Url
$exportObject.Id = $list.ID
$settings.FileLocation = "C:\Temp\BackupRestoreTemp\"
$settings.BaseFileName = "ExportList-"+ $list.ID.ToString() +".DAT"
$settings.FileCompression = 1

Write-Host "FileLocation", $settings.FileLocation

$settings.ExportObjects.Add($exportObject)

$export = New-Object Microsoft.SharePoint.Deployment.SPExport($settings)
$export.Run()

$web.Dispose()
$site.Dispose()
}

function Import-List([string]$DestWebURL, [string]$FileName, [string]$LogFilePath)
{
[System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint") > $null
[System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint.Deployment") > $null

$settings = New-Object Microsoft.SharePoint.Deployment.SPImportSettings

$settings.IncludeSecurity = [Microsoft.SharePoint.Deployment.SPIncludeSecurity]::All
$settings.UpdateVersions = [Microsoft.SharePoint.Deployment.SPUpdateVersions]::Overwrite
$settings.UserInfoDateTime = [Microsoft.SharePoint.Deployment.SPImportUserInfoDateTimeOption]::ImportAll

$site = new-object Microsoft.SharePoint.SPSite($DestWebURL)
Write-Host "DestWebURL", $DestWebURL

$web = $site.OpenWeb()

Write-Host "SPWeb", $web.Url

$settings.SiteUrl = $web.Url
$settings.WebUrl = $web.Url
$settings.FileLocation = "C:\Temp\BackupRestoreTemp\"
$settings.BaseFileName = $FileName
$settings.LogFilePath = $LogFilePath
$settings.FileCompression = 1

Write-Host "FileLocation", $settings.FileLocation

$import = New-Object Microsoft.SharePoint.Deployment.SPImport($settings)
$import.Run()

$web.Dispose()
$site.Dispose()
}

Usage:
# For Export a specified SharePoint List
Export-List "http://mySharePointWebApplication/sites/MySiteCollection/MyListToExport/"

# For Import the list you export in previous command
Import-List "http://mySharePointWebApplication/sites/OtherSiteCollection/" "ExportList-TheGUID.DAT" "C:\Temp\BackupRestoreTemp\ImportLog.txt"