##Note - This question applies to Minecraft 1.5; for newer information see this question.
I'm covering everywhere near my house with my torches and building walls (using fences or blocks) around them, to make sure no creepers blow me up as I come out, or trample my sugar cane and wood. (I have now completed about 80% -- without using any mods, tools, or other cheats)
However, as you can see, the tops of some trees are too dark. So I'm worried about monsters spawning on the top of trees. There's some mention about leaves and mobs in Minecraft Wiki:
...and they never spawn on Glass, Ice, Stone Slabs, or other see-through or non-cube blocks.
(I'm playing Minecraft in fancy mode.) Even if monsters can't spawn on the leaves, maybe some monster can spawn on the wood that's not covered by leaves.
(Don't mention about spiders -- since they can climb fences as you know and I don't care about them)
Can monsters exist near my house?
The distance between my torches is 5 metres.