I've been making some posters, I've done 2 so far, the 1st uses nice Web 2.0 rounded corners and some images found on google image search that have been played with in PhotoShop and then converted to curves in Inkscape and then send back into PhotoShop.
The 2nd is based on the cover for a DVD I saw online. Again I pretty much only used Inkscape and PhotoShop and I'm well impressed with how well they work with each other too!