Here's one from TLC Incredible Weddings. The bride lights up her gown a key moment in the first dance.
This gown isn't strictly for a wedding, but has far more interesting lights.
I wonder if it can spell out words? Like I DO in giant letters - similar to a Jumbotron thing at a sports game. That would be funny. In addition to LED lights, this dress is also coated in Swarovski crystals.
If you want to incorporate a more tasteful amount of blinking, flashing lights into your wedding, you could just order a light-up garter.
I even have the perfect first dance song to go with these gowns. Hardehar.