I would like to see the addition of concrete. It could have the same texture as clay blocks, so less work involved, but here is how it would differ: When poured out of a concrete bucket, the concrete spreads out like water, and then hardens into solid blocks. This would be great for fast construction of small structures such as floors and foundations, and would give us a better use for gravel than "that crap you use to block up lava."
sand + gravel + water bucket equals...