Ampad makes a very nice pull and seal envelope in the catalog size (9" x 12"). They come in an easy-open dispenser box, and they are great for sending a number of pages that you cannot fold and put in a smaller envelope. They are made of a 28 lb heavyweight white wove, and what I especially like is the fact that you just pull off the adhesive strip to seal them.
The paper these envelopes are made of is a nice, heavier consistency, so you know that whatever you are sending will be protected. Of course, if you are mailing anything breakable, like CDs or DVDs, you might want to use a bubble mailer for that. But I use these envelopes for papers that I am sending out that are of a certain thickness and cannot be folded. They fit very nicely in this type of an envelope, and the box I have contains 20, so I know I will have them for while.
I have other Ampad products as well as these envelopes. They serve me well and have always given me good service.