I have three crochet afghan projects in progress. The newest one is done in a diagonal box stitch pattern, which I've never done before. I think it may end up being my favorite pattern to do so far...not so much for the looks of it, although it's very nice, but I just like doing it. It's different, even though it's mostly only Double Crochets, Chains, and Slip Stitches.
Here is a Box Stitch Tutorial. I found it after I had struggled through on my own. It's another one of those patterns that doesn't seem like you're doing it right until you get a few rows done, at least for me.
Here is a picture of a finished one that was posted on Crochetville the other day:
Credit for this photo and afghan goes to Bearland53 over at Crochetville.
And here's a totally different-looking one that is made using the exact same pattern, just different colors and row variations:
I got this picture HERE (pdf file), along with the pattern. You won't find the pattern using the link in the Crochetville post.
Mine looks more like the first one, but you can't see it until it's done. No peeking! I'm using Bernat Berella "4" in Dark Oxford (Gray), which is impossibly soft, and RHSS in Ranch Red (a deep brick red). It's purdy. Barnaby has already claimed it as his because he likes it so much. I'll definitely be making more afghans with this pattern. It seems to work up very quickly.