<p>Is there an easy way to verify that a given private key matches a given public key?  I have a few <code>*.pub</code>and a few <code>*.key</code> files, and I need to check which go with which.</p>
<p>Again, these are pub/key files, DSA.</p>
<p>I would really prefer a one-liner of some sort...</p>

Encrypt something with the public key, and see which private key decrypts it.
This
Code Project article
by none other than
Jeff Atwood
implements a simplified wrapper around the .NET cryptography classes. Assuming these keys were created for use with RSA, use the asymmetric class with your public key to encrypt, and the same with your private key to decrypt.