Equivalent to C#'s "using" keyword in powershell?

There's really nothing at the namespace level like that. I often assign commonly used types to variables and then instantiate them:

$thingtype = [FooCompany.Bar.Qux.Assembly.With.Ridiculous.Long.Namespace.I.Really.Mean.It.Thingamabob];
$blurb = New-Object $thingtype.FullName

Probably not worth it if the type won't be used repeatedly, but I believe it's the best you can do.

Check out this blog post from a couple years ago: http://blogs.msdn.com/richardb/archive/2007/02/21/add-types-ps1-poor-man-s-using-for-powershell.aspx

Here is add-types.ps1, excerpted from that article:

param(
    [string] $assemblyName = $(throw 'assemblyName is required'),
    [object] $object
)

process {
    if ($_) {
        $object = $_
    }

    if (! $object) {
        throw 'must pass an -object parameter or pipe one in'
    }

    # load the required dll
    $assembly = [System.Reflection.Assembly]::LoadWithPartialName($assemblyName)

    # add each type as a member property
    $assembly.GetTypes() | 
    where {$_.ispublic -and !$_.IsSubclassOf( [Exception] ) -and $_.name -notmatch "event"} | 
    foreach { 
        # avoid error messages in case it already exists
        if (! ($object | get-member $_.name)) {
            add-member noteproperty $_.name $_ -inputobject $object
        }
    }
}

And, to use it:

RICBERG470> $tfs | add-types "Microsoft.TeamFoundation.VersionControl.Client"
RICBERG470> $itemSpec = new-object $tfs.itemspec("$/foo", $tfs.RecursionType::none)

Basically what I do is crawl the assembly for nontrivial types, then write a "constructor" that uses Add-Member add them (in a structured way) to the objects I care about.

See also this followup post: http://richardberg.net/blog/?p=38

this is just a joke, joke...

$fullnames = New-Object ( [System.Collections.Generic.List``1].MakeGenericType( [String]) );

function using ( $name ) { 
foreach ( $type in [Reflection.Assembly]::LoadWithPartialName($name).GetTypes() )
    {
        $fullnames.Add($type.fullname);
    }
}

function new ( $name ) {
    $fullname = $fullnames -like "*.$name";
    return , (New-Object $fullname[0]);
}

using System.Windows.Forms
using FooCompany.Bar.Qux.Assembly.With.Ridiculous.Long.Namespace.I.Really.Mean.It
$a = new button
$b = new Thingamabob

Thanks everybody for your input. I've marked Richard Berg's contribution as an answer, because it most closely resembles what I'm looking for.

All your answers brought me on the track that seems most promising: In his blog post Keith Dahlby proposes a Get-Type commandlet that allows easy consutruction of types for generic methods.

I think there is no reason against exetending this to also search through a predefined path of assemblies for a type.

Disclaimer: I haven't built that -- yet ...

Here is how one could use it:

$path = (System.Collections.Generic, FooCompany.Bar.Qux.Assembly.With.Ridiculous.Long.Namespace.I.Really.Mean.It)

$type = get-type -Path $path List Thingamabob
$obj = new-object $type
$obj.GetType()

This would result in a nice generic List of Thingamabob. Of course I'd wrap up everthing sans the path definition in just another utility function. The extended get-type would include a step to resolve any given type agains the path.