i have a new comet and was wondering what type of plants are best??

it depends on your lighting, water temp, ph etc. check out http://www.kokosgoldfish.com/Plants.html for some ideas. most of the plants on that link are quite easy to care for.
This is a handy website too guide to planting a tank - plantgeek.net

personally i prefer broad leaf plants such as anubias and java fern as they are easy to care for, dont require lots of light, and goldies are less likely to eat them as the leaves are thicker. Common coldwater plants such as anacharis are good for goldie tanks, but will get munched on (and possibly destroyed) by greedy fish, especially comets/commons (it can be like installing an all you can eat salad bar in your tank lol!!)

none of these plants are particularly expensive, and can be tied to driftwood/ornaments, or potted/rooted in gravel (making sure to bury only the roots and ensure the rhizome - the big bit where the stems grow from - is not buried as it may rot/die)

hope this helps

I have also found cryptocornes and java moss to work well with commons, comets and shubs, along with the plants suggested by katmad

Anubias!!! I want one. That's what Koko keeps in her tank, and her fish don't gobble it down. My fish have never turned down a plant, but supposedly, the anubias will be harder for them to tear up.