Tips for next photography purchase? Lens.etc?

I've been shooting with my canon t2i for about a year and a half now, with a 18-55mm and a 50mm 1.8 lens
(before that i used a nikon d60 with kit lens)
and i'm looking to expand my photography kit and start maybe doing some business so i want some equipment that can produce even bigger quality results (i know its not the camera but the photographer blah blah whatever) i've never been quite good at choosing equipment myself
but i was looking for some suggestions
i like to do mostly
portraits and experimental shoots
fashion
and some landscape and wide angle stuff
i've also realized i could use a flash or an external light source
+ maybe some lens protectors?

could you recommend me some items from all the things i just mentioned? In your opinion?
i could say i'm in a money range but from what i've seen all the good things are over 300 which you know, whatever, just keep it less than 600: d

If you find yourself wanting to put more of the scenery in the shot like in landscapes, get a wide angle lens, wider than 18mm. If you find yourself wanting to get closer still after walking towards your subject like in fashion shoots, get a longer lens, longer than 55mm. If you find yourself wanting more light then get a strong enough flash gun. Go to http://bhphotovideo.com/...ovideo.com to do your window shopping.

If you are doing landscape photography, get a quality tripod.