Well firstly, you should search before posting, you've pretty much missed out on quite alot. However, to save time, here are some good plugins to use:
Tank throws special infected (chance):
http://forums.alliedmods.net/showthread.php?p=1320927
Silent infected:
http://forums.alliedmods.net/showthread.php?p=1291714
When punched by tank u loose your gun:
http://forums.alliedmods.net/showthread.php?p=1298067
When you kill tank/witch meteors fall from the sky:
http://forums.alliedmods.net/showthread.php?p=1274646
Tank powerups:
http://forums.alliedmods.net/showthread.php?p=1202855
Remove medkits/weapons/whatever you want:
http://forums.alliedmods.net/showthread.php?p=1004457
Randomize witch/tank hp:
http://forums.alliedmods.net/showthread.php?p=1076665
Well. There are a load more of plugins which change infected to make them harder and stuff. However go use the search bar, and search for the sutff you need, for example type in tank or realism or witch (that stuff)
To learn a plugin you gotta read the big boring bad ass wiki:
http://wiki.alliedmods.net/Introduct...rceMod_Plugins
One more thing, you might also want to use this to search for plugins, I tend to find it eaiser as it shows all plugins you want to find on one page:
http://www.sourcemod.net/plugins.php...tion=&search=1