If you don't want to bother buying lens filters or making your own, you can still produce vignetting effects with your normal photos using post-processing software. There are various custom tutorials on how to achieve this, but if you want a quicker way, although with limited capability, you may use Adobe Photoshop's Lens Correction Filter Tools.
To do this, open a sample photo, then select Command - Filter - Distort - Lens Correction. A new dialog box will appear and you can see one option as vignette. Simply adjust the slider whether you want to increase the darkening or lightening effect on your photo. You can also adjust the Midpoint to adjust the vignetting effect at midpoint.
For more advanced vignetting process, you can find tons of resources on the web featuring tutorials and workflows on how to achieve vignetting effects on your photos.