Think about what kind of look you are going for
This is a small company that actually hand makes invitations, so designs are flexible.
BASIC $$-$$$ Flat printed main invitation card + a white RSVP card. I use a 90lb matte white card stock that works well with photo quality printing, and the envelopes are 80lb white peel-n-press. This will hands down be your most cost effective option. Stick with a 5x7 inch main card, get a longer/taller 4x8 inch card, or even go with a square shape. You can add as many inserts/extra cards as needed (reception, direction, hotel, website, etc) though of course that will add to the pricing.
STEP IT UP $$$ If you aren't doing full background printing or photographs, a color card stock could work very well. Including *shimmery* card stocks! Color envelopes are also available, and yes, custom printed envelope liners are also an option.
LAYER IT $$$ Layer two cards together for a higher end invitation. You will have one printed card attached to another card. The backing card is usually going to be a color, and yeah, metallic card stock is a very popular option for the backing layer (why do black when you can do Onyx?). Glitter card stock is also an option here. Glitter card stock has more of an actual glittery texture VS the more demure shine of a metallic card stock.
FOLD IT $$-$$$ Bi-folds, Tri-folds and Petal folds! Or better yet, a Pocket fold! Pocketfolds can have mutiples sizes, shapes, colors, and they work well with 1-3 inserts.
ADD IT $$-$$$ Printed paper wrap arounds are a popular addition for basic invitation sets; The whole set is held together and then the guest breaks the wrap. Return address printing on RSVP envelopes is usually also an option, and yes, you could even get guest address printing. Another thing that can be added is rounded corners.
BERIBBON $$$ There are a few different ways to use ribbon. Wrap a ribbon around a pocketfold, or have it threaded through the side of a folded card for a bow.
UPSCALE $$$-$$$$ Foiling & letterpress are available; I will work with a partner or two to make something like this happen.
Magnetize $$ Save the Date Originals does primarily make save the date magnets! So, yes, you can get a magnetic wedding invitation. Or, you can have a magnet added in as part of your wedding invitation set.
Things that STDO doesn't usually do include... buckles, glued on rhinestones, postcards, seal-n-sends, and scrolls.