Are you looking to do physical or digital wedding invites?
If you are aiming for digital. I sent mine through Green Envelope. The site provides TONS of templates or you can create one completely from scratch. You can also design you envelope and this would be sent via email to your guests.
I went with these simple black and white invites from Etsy! I wanted romantic and modern and to add some colour I put in the floral envelope liners (great option if you want to add a little something without being overwhelming not to mention they really popped against the black envelope; love the way they turned out!). Good luck! (doing the design of the invites was one of my favourite parts of planning).