Some of the nicest, albeit most expensive, paper available is a new paper that has a metallic sheen, and is guaranteed to be printable. Metallic papers come in silver, gold and copper. There are also variations of these colors, incorporating purples, blues and reds. Metallic paper is the newest thing on the scrapbooking market, and many companies are working hard to create the foiled look for contemporary designs. A search of a quality scrapbooking web site will provide you with information and pricing on metallic paper (and many other options for creating your invitations, as well!)
Vellum is a type of paper that is commonly mistaken for tracing paper, and while similar, is actually a type of decorative, opaque paper that comes in a variety of weights and colors and is very popular for wedding invitations. It makes an excellent outer layer for the invitation because the lighter weights are translucent, and make it possible to either print, or display clip-art designs under it.
Handmade paper provides a shabby-chic style of invitation that, while less traditional than cotton or linen paper, has become trendy. Handmade paper includes all papers that have been embellished by hand, with additions such as dried flowers, rubber stamps, watercolors, and any other designs. A nice way to use handmade paper is to place it behind the card stock, which the invitations are printed on. The handmade paper becomes a border, or frame, for the invitation. If it fits your budget, try even another layer, with two different handmade papers behind the cardstock. The more layering, the more elegant your invitations will appear. Just remember to keep the designs simple when layering, and make sure the papers coordinate with eachother. Ask a friend or two for a second opinion, if necessary.
Another design option is to print a picture on a plain piece of card stock and cover it with a sheet of vellum that has your invitation details printed on it. Use a ribbon and punch holes in the cardstock and vellum to attach. This creates a nice and simple invitation that is easy to make, but looks intricate, fancy, and professional.
Visit a print shop, scrapbooking store or a craft shop browse the papers available. Some of the most popular, traditional choices for paper and card stock include recycled, cotton and linen. Recycled paper is the least expensive, and available in many colors. If you are shopping online, it still pays to visit a store so you can get a good look and feel for the type of paper you're choosing before selecting it.
Your paper choices can be limited by the type of invitation you are creating. If you are designing them on the computer using clip art, you will want to make sure the paper used for printing on will fit through your printer and that the ink will adhere without bleeding. Cotton or recycled paper or thin card stock is good for this process. Linen or parchment paper, or thick card stock, may not work as well.
Envelopes are another important decision. Primarily, you want to make sure the color and materials match the paper on the invitation as best as possible. Often, you can get a matching color, but with added flair, such as a foil lining. This option adds elegance and also makes the envelope sturdier and allows for added protection during mailing.
Remember to order enough paper and envelopes to make extra invitations, in preparation for last minute invites and to add to your wedding album or scrapbook.