I've found blackburn type folding mirrors to be indispensable when riding in the big smoke. Being able to quickly fold them down to get between cars blocking my way is great. I've recently discovered that if you tape one of those tiny LED lights to the end of your mirror it is great at night. Seems to keep passing traffic quite a bit further away from you. I have it facing backwards for passing traffic, but you could have it forwards if you prefer, or one light each way even, if you really want to get carried away.
Ryano