As if Photoshop wasn't overwhelming enough, there are tons of plug-ins that you can buy to help you do amazing things. The trouble is, where do you find these great plug-ins?
One of the best places is Plugs-N-Pixels. It's basically a "one-stop-browsing" site to see different plug-ins and what they do.
So instead of bouncing all over the Internet looking at different plug-ins, try Plugs-N-Pixels first.
The site also produces a free e-zine that goes more indepth on these plug-ins and lets you see how they can be used.
For direct mail, I find most plug-ins a bit of overkill. But every-so-often, you see a plug-in that either does something automatically that you had been doing manually (thus, saving you time), or you find one that sparks your creativity and is useful for a future project.
It's just good to know what's available to you.