I love weddings that have slide shows (although as they are rarely on slides anymore that probably isn't the best description). I love watching the bride and groom grow up, meet, and fall in love, via pictures. The slide shows are often professionally produced, sometimes part of a photography package. However, with a little modern technology, this is something you could easily create on your own - for free!
And that is not to say that you could create some obviously home-made presentation. Easy-to-use software that is likely already on your computer will allow you to turn out a professional looking slide show in record time:
Step 1: Gather pictures and scan them into digital files - this is the most laborious part of the process and I promise it is smooth sailing from here.
Step 2: Check to see if your computer has a movie editing program, such as Windows Movie Maker, already installed on your computer - most newer computers will and you just might not have noticed it before.
Step 3: Load all of the pictures, music, etc. you would like to use into your program.
Step 4: Arrange your pictures in the order you would like them displayed. Hint: There are typically two views in which you can create your project - Storyboard and Timeline. Storyboard is useful for getting your pictures in order to begin with because they are easier to see, as well as for adding transitions and special effects. Timeline is useful for adding audio tracks so that you can align the stop and start of different audio with various pictures.
Step 5: Add the finishing touches with title slides, transitions, effects and music.
Step 6: Publish your project as a movie, burn to a DVD and you are ready to go!
To give you an idea of what the final results can look like, check out the below movie. Although it was created for a 50th birthday rather than a wedding, it will give you an idea of the type of slide show you can create yourself: