A pretty standard set of tiles..

[havocplague]

Since I've started working on a tile engine for a small project, I thought it would be a great way to get back into doing pixel graphics. I started working on them a couple of nights ago, along with the engine itself, just so that once I get around to testing it, I have something to test it with. It's pretty bland now, and the tiling on the grass itself is horrible, but I'm hoping to work that out soon. I was also hoping that someone could give me an idea of how to texture my dirt, to make it  more.. Well, dirty. A few of the tiles are also mirrored, as this is a feature of the engine, but I'm not sure if I want to do that once I get the actual tiles done, other than for the sake of being able to.

Not much to c&c yet, but I'd just like to know if I'm at all going in the right direction, now that I'm just getting started. It's a lot easier to change an error early on.

tiles <- -> almost identical tiledemo

[Rydin]

The first thing that sticks out, or rather doesn't stick out, is how the upper levels blend with the lower.  I think the quickest fix for this would be some shadows, but it's not necessarily the most effective fix...you may need to look into it more.
Next, I'd like to say that the "grid" is apparent.  Luckily, the tiles look like they could easily be fixable...some copying and pasting could do the trick.
Lastly, you say you want your dirt to look more "dirty", but it seems as though you are already on the right track; just continue what you've got going with texture-y dirt tile and you should be fine.
I can see these tiles going places, and with enough work, they could be phenomenal.  Keep pixelling!