We ordered our invitations from Apropos in Greenville, DE.  They do not have a website, so don't look it up :)  They want you to come in, and want that relationship with their customers (something you don't see much nowadays). 
Our invitations were William Arthur.  We ordered the invitation, the inner lined envelope, the outer envelope, the RSVP/response card, and the Response Card Envelope.  We were trying to keep cost down, so we nixed the Reception card in favor of putting that info on the invitation itself.
We went with William Arthur for several reasons: one, I really liked the weight and feel of the products offered.  We had looked at Carlson Craft, but were not impressed with the quality of their product (I also didn't like that the RSVP card was a flimsy fold over, instead of being a solid weight single layer card).  Second, they had many more options than any of the other companies.  The invitations we ordered were very simple white invites, but because William Arthur offered many customizable options, we were able to make them look the way we wanted.  We were able to customize the font, the color of the font, the border, the inner envelope liners, the motif on the envelopes...By customizing them this way, we were able to save money and make them our own.  Third, they offer sales.  We were able to get 100 invites for the price of 75 because of the special they were running.  Overall, we were very pleased with the company William Arthur.
Apropos was very helpful in staying within our budget, giving us guidance in terms of etiquette, and were very prompt on fulfilling our order.  We had our invites with two weeks of placing the order.
We decided to do the invitation inserts ourselves.  We got white cardstock for a great price, and printed them on the high quality printer at Brian's work, matching the ink to the invitations.  We included hotel info, directions to the church, directions to the reception hall, as well as our wedding website for guests.

Escort Cards

When we attended my cousin Jennie's wedding in July 2009, I fell in love with her escort cards.  Instead of doing regular tented escort cards, she did the enveloped kind.  I loved not only the elegance of it, but how it could save time and money.
Basically, the name(s) of the person/couple are listed on the outside of the envelope, and the inside contains a card that reads "You are seated at Table 3" or just a "Table 2" (or whatever table they are at).  This helps to save time and money because if we need to switch tables around, all I have to do is switch the inner cards instead of printing and taking time to make a new tented escort card.  And anything that saves me time and money, while being elegant at the same time, is alright in my book.
Crane & Co. sells a set of these, but you can find them online (with some searching).  These used to be the way that escort cards were always done (tented style was saved for place cards, which were put directly on the table and told a person which chair to sit in, not just the table).  But, the tented version soon took over.  It does take some finagling, but you can find them.  You can also make them yourself, as they do sell the envelopes and cards by themselves- and the envelopes are available in color!