As it becomes more and more common for photographers to offer high resolution files and digital negatives, it also seems to become more common that photographers are willing to completely give up their rights to their own images! You should never give away your copyright to your own work - unless you're selling it for a very hefty price and it's work that you don't need to be recognized for (as is the case with some stock or commercial work). In the case of portrait and wedding work, which you may want to include on your website or in your portfolio, you need to maintain your copyright protection on your images if for no other reason than to prevent others from claiming your work as their own.
One of the easiest ways to protect your rights is to include a Creative Commons License on the disk with your images. There are several different levels of the creative commons license which are customizable for different situations. My preferred license looks like this: Attribution-NonCommercial-ShareAlike. By providing this license instead of a full copyright release, I am able to protect my own rights to the image, while still allowing my clients the ability to print and display the images for personal use. As an added level of protection, you can easily embed your copyright information in the metadata for each image upon import or export with programs like Bridge or Lightroom.
While all original work is automatically protected by copyright laws upon creation, there may be times when it is necessary to register your copyright. For example, when submitting your work for publication, or when photographing a celebrity or historical event in which your work may end up being widely distributed or highly sought after.
It would also be nice if we, as a community of photographers, could agree on some common language when referring to these different types of files made available to the client. In an effort to establish some kind of consistency, here are my proposed definitions along with some benefits and drawbacks to offering each to your clients:
Digital Negatives - these files are straight-from-camera files, exactly as they were captured, with no color correction, editing, or cropping. If files were captured in RAW, they are delivered in RAW. If files were captured in JPG, they are the original files as captured in sequence. By providing this type of file to your client, you are providing an unfinished work which can be both good and bad. On one hand, a client may realize that they are unable to process and print the images on their own (as could be the case with RAW files) and will need your assistance before creating any prints, on the other hand a client may take your unprocessed images and present them to others as a final work, which may in turn degrade the overall perception of your work.
High Resolution Files - generally considered to be at or above a resolution of 1200x1800 pixels, these files may be color-corrected, toned, cropped, etc. and are saved in a print-ready format such as JPG, GIF, or TIFF. Since these images are print-ready, there's a lesser chance of them being altered in an unfavorable way, however you still cannot control the calibration of the monitors or printers that your client is using to view or print the images.
If you're going to offer either of the above options to your clients, it is very important to educate your customers about the differences that can result when printing from uncalibrated monitors and printers, as well as the difference in quality between the products you provide and the products that they may purchase on their own. I highly suggest making sure that your clients are receiving finished prints or an album BEFORE receiving their files. This ensures that you've had a chance to print a product to your expectations before your client produces something on their own that may be a substandard product. You work hard to create your art and it is up to you to make sure it is being presented in the best possible way.