http://dev.bukkit.org/server-mods/mobcatcher/

This is a very neat plugin that I found on Bukkit.Dev, I saw EmperorMyrf post about spawning eggs so here it is.

MobCatcher allows players to capture mobs and get the corresponding spawn eggs. This is useful for trading and transporting mobs from player to player or even across worlds. As well as having a configurable capture item, MobCatcher also boasts configurable mob types and item costs per capture, bringing a new economic value to mob types both peaceful and hostile. MobCatcher is able to store and recall mob specific data saved to specific spawn eggs. This means things like capturing and spawning colored sheep, baby animals, and tamed wolves is possible! This is done via a separate .dat file which saves data for each mob and removes it when that mob is spawned.Try it out on your server today!

I was just about to post about this hopfully a mod or admin will see it

First I think this would cause way too much lag, especially if like it says it stores the data of every single mob someone catches. Now multiply that by the 100+ people who play daily. Our lag that we currently have would suddenly spike up far too high.

It also would be far too easy to get mob eggs. That wasn't the point of what the mods and admins wanted. That's why we have spawn eggs limited to the forum shop as well as drop parties and such, because it makes it hard to obtain them. This way it would be far too easy for just anyone to go around getting them.

The admins/mods also didn't want to allow hostile mobs like this, they only gave us the option to change spawners for passive mobs because of the despawning problem the server has because of how it spawns and despawns things to keep lag low.