With Tortoise SVN:
If you haven't committed your changes yet, you can do a revert on the parent folder where you deleted the file or directory.
If you have already committed the deleted file, then you can use the repository browser, change to the revision where the file still existed and then use the command Copy to... from the context menu. Enter the path to your working copy as the target and the deleted file will be copied from the repository to your working copy.