I would wait a while before adding the plants as they can be a little sensitive to the ammonia and nitrites as well as the fish and you can put them in as the cycle process progresses. Some good low light broad leaf plants for bettas to sleep on include Sword Plants, Java Fern, and they will also like Duckweed (it just floats on top of the water - so just get enough to cover no more than 1/6 of the tank surface). Some shorter plants they like are Anubias Nana, Anubias Coffeeola, Wisteria, Java Moss (kind of messy - has to be tied down to a rock or something). My bettas favorite plant grows from a bulb and is called a Madagascar Lace Plant and is a beautiful plant but takes up a lot of room and takes some care. You can look up most of the plants on
http://www.PlantGeek.net That site tells you what the plants need for lighting, where they need to be planted in the tank and what they are like and in most cases has good pictures of the plants of them.. Most of the ones I listed above should be pictured there.
Rose
The pictures below have most of the plants I mentioned in them. Marty has the Anubias plants in the front of his tank and NoeL has a Sword Plant in the Back of his tank and The Madagascar Lace Plant on the other side of the tank.