Video Converter
Well i'm not gonna post any software you need to buy because i've had experience with it and it really isn't worth it. In fact, I will show you freeware which is just as powerful and in my personal opinion way better and faster!
http://www.videora.com/en-us/Converter/iPod/
I have just started to use this software and it already has grown on me. It's fast and easy to change the settings. If you are experienced you can even go further and go into Advanced Mode to muck about even more in the details that you want.
Ringtone Maker
I also found an easy way to get any full song as your ringtone. This works very easily and I recommend it to everyone who wants a custom ringtone!
http://235sr.23.funpic.de/RingmiTone/index.php
Wallpapers
I don't really care for wallpapers but there are a few sites around which have some cool pictures you can use, some are :
http://www.iphone-wallpapers.us
http://www.iphone-wallpapers.net
http://www.sciphone.net
I also found going through DeviantART a good idea as there are A LOT of designs you can choose to use as a wallpaper. I recommend you check Videa's designs out as he tends to create some awesome 3D models :
http://videa.deviantart.com/gallery/
I plan on adding to this as the media needs develop but these should get you started!
