Per some requests, here are a couple shots of the tiles I created with official Carcassonne tiles.
Here I have JPutt's Season's expansion tiles along with one of his Witches & Wizards tiles played along with official Carcassonne tiles.
In this shot, I show a Windmills and Bakery tile side by side with an official tile.
In this shot I tried to show the similar size and thickness between the two. I did stagger the two tiles just slightly to show similar edging.
Here is the Season's expansion, with a few condition tiles on the condition board
The full Lake expansion. (The only reason there are slight lines on the large lake tile are because my printer was on the incorrect setting)
Finally, a picture showing the Chariot Racing expansion. I have a small bag that I use to draw the race tiles from.
I use full sheets of sticker paper that I print on and then adhere to the chipboard (in the US, chipboard is basically the same material that the official Carcassonne tiles are made from). I then cut the squares out by hand with scissors. I am normally quite picky but I find that this method holds up well.