Several gamers on the internet have created many 4e monsters. But the pace of production is slow, at best. And there seems to be only a few places that have focused on compiling monsters for 4e. The first place I found is the Monsters section of ENWiki over at ENworld. Another place I found 4e monsters is at the WotC forum thread, 4e Monster Compendium. If there are other places, please let me know.
So what am I going to do? Well, as I said, I'm putting together my own house rule monster book. To this end, I've made up a list of all the monsters in the 1e Monster Manual and I'm systematically finding any 4e versions of those monsters on the internet. I've been able to find several of them. But many more have yet to be made. So I'll try to make a few of my own.
In the 4e Dungeon Master's Guide, there are rules given for creation of original monsters. Thankfully, this system is less ambiguous than any of the previous editions. New monsters can have its combat statistics clearly defined from the outset and further details can be ironed out by looking at similar examples in the 4e Monster Manual. Defining the powers is the tricky part. But it's far from impossible.
I will create a single entry on this blog that I will bookmark and periodically update. It will contain a list of all the monsters in the 1e Monster Manual. Each entry will link to known home brewed 4e stats for each monster. Some of them will link to monsters that I create myself. Others on the internet can bookmark this blog entry and link to it. This will be an experiment and I don't know how well this will work out. If it doesn't work out, it's no big deal. Ultimately, I might have to move the list to a proper web page on my own web site.