You asked a question which probably lots of people ask themselves when buying their first DSLR.
Kit lens looks like a huge improvement when you switch from a point & shoot camera to an
DSLR at least it looked so to me :) This lens has some advantages as well as disadvantages, however every lens has them both. Canon 18-55mm lens is useful in the way that it has different focal lengths, so you can take it with yourself for trips, use it for urban photography and even portraits. But one of the minuses is in the f-stop which changes when you zoom in or out.
Canon 50mm 1.8 II is a great little lens, I have this lens too and I love it, but it also has its limits. If you have limited space, it might not allow you to take a photo you want, because on cropped sensor cameras this lens is around 80mm. However it's a very sharp lens and and lovely bokeh can be created with it.
If you are interested in more detailed information on these two lenses and see photo examples, please check my user reviews for these lenses:
Canon kit lens: http://dinablaszczak.hubpages.com/_stxprf1/hub/CanonEFS1855mmf3556ISuserreviewwithimagegallery
Canon 50mm 1.8 II: http://dinablaszczak.hubpages.com/_stxprf1/hub/Canon50mm18RevieworFactsaboutNiftyFifty
I'm also familiar with Canon 18-135mm lens and I can say that in my opinion this lens is of a sufficient quality if you plan to take photos for your own pleasure, rather than for business, like stock images etc.
Can't say much about Canon 55-250mm as I never owned this lens, only tried it out once in a shop. It has a nice zoom and I guess it would be useful if you wanted to take photos of birds or further away objects.
So my conclusion is that if I had to choose, I would choose option of Canon 50mm 1.8 II + 18-135mm lens :)