Name: Umm.... leaves in macerator gives saplings?
Description: Ever cut down a tree with a chainsaw? Well I'm sure you have since that's the point. But if you've cleared the leaves with the chainsaw too, you get all these leaf blocks too (and some saplings and whatever else those leaves drop). If you've got plenty of saplings of that kind of tree, you'd probably find some way to dispose of these leaves: toss in lava, recycle them, make plantballs. If you didn't have enough saplings, you might take advantage of a quirk of the chainsaw and keep placing the leaves and chopping them down, since you'll always get the leaves back plus the occasional sapling.
I propose, why not let a machine do the latter process for you? Just throw the leaves in a Macerator, and it will chop up the leaves until it finds and spits out a sapling. It won't find a sapling in every leaf block; rates should be somewhere between 1 in 20 for ordinary chopping / decay and 1 in 2 to prevent energy profit. If I had to pick a number, I would pick 1 sapling in 5 leaves, but that's subject to balancing of course.
Recipe: Leaves > (macerator) > Saplings (between 2 and 20 leaf blocks per sapling, on average)
On a similar note...
Name: Tall Grass / Shrub / Fern + Macerator = Seeds
Description: A logical extension of the above suggestion, you also get tall grass (etc.) as items from the chainsaw (why? eh idc). So if you can macerate leaves to get saplings, you should be able to macerate tall grass to get seeds. Clearly it would have to be balanced differently since the energy considerations are different; it could go as high as 1:1 I suppose. Though I guess it's not terribly useful, it is quite logical.
Recipe: Tall Grass > (macerator) > Seeds (at some percentage chance, possibly as high as 1:1)