Top right is inching on okay, top left and bottom right should be thrown out, do you see how the edges do not blend with the rest of the texture? you can see the grid and the icons look like they have edges. Also I do not even understand what the bottom right one is supposed to be. For grass you are using poor color choices, pick around 3-4 palette colors which are less contrasty (similar rgb) and try to use as little noise as possible to convey texture.

These are decent but can be improved greatly. I recommend having a good read of this: http://gas13.ru/v3/tutorials/ sywtbapa_almighty_grass_tile.php
I'm not even an iconner but it does help.

I have a tip for you, once you do what looks like a good tiling Icon, use the arrow shifting feature to shift the icon 16 pixels left and 16 pixels down. This will ensure your edges blend and you can fix the seams that look like a giant + sign in the middle of your icon and things will blend better.

Of course you did.

Anyways, it looks like crinkled construction paper. Invest your time in some tutorials that will show you how to create proper texture.

Waterymonster, that is still an improvement. I recommend trying what I suggested above with shifting the icons and fixing the grid problem as others have pointed out.

http://imageshack.us/photo/my-images/163/spritingtut.png/

Look at spriting tuts,heres one i made while ago its simple the way i like my crass tiles.