I don't know of any but imageshack can let you upload a 1mb image http://imageshack.us/ Why would you need a 4mb image???
Well I got a 1 gb hosting place from supremepixels so I don't use any others, but I would suggest imageshack or photobucket
use a general host, try 1asphost [>>here<<] they have a 100 mb limit i beleive and under request unlim B.W
I would say deviantart, but it doesn't seem to be working for me right now. Just out of curiosity, what image are you uploading that takes up 4 mbs?