I wanted to share a quick tip for you that discovered thanks to this post on Focus Faction, updated below for Photoshop CS6 (the menu is now in a different place). This is the fastest and easiest way to create a vignette for your photos in Photoshop in just a few seconds. It has saved me a lot of time.
1. Go to Filter » Lens Correction…
2. Click on the Custom Tab
3. Under the Vignette section, move the amount slider to the left towards “darken” and adjust the midpoint slider to suit your needs.
Voila! A simple vignette in just a few seconds.