Just a quick map I made in MCEdit. 


Basicly I put the nether underneath the standard overworld, replaced the netherrack with standard overworld ore, then duplicated the edges with the clone tool and mirrored them while sloping them downwards. Finaly, I added the lake of lava for cinimatic effect and dramatic flair.

I'm thinking I might use this, or somthing like it as part of a future server, but you're more than welcome to use it yourself if you give credit on your server. If you do end up using this on your own server feel free to post your IP in the comments so I can take a look and see how it turns out. This isn't a complete spawn area, but it is a good starting point for you to construct your own spawn area, or an adventure map.