Our rule is simple, no mods except for Optifine.

If you're afraid to lose your mods, simply backup your modded minecraft.jar and use a fresh .jar for the server.
Then just replace the .jars when you want to use the mods for singleplayer or another server.

Why would you allow optifine but no other mods? the most of the mods, save for 2 do not work, toomanyitems only works for me when I'm an admin/op, and inventory tweaks doesn't work, so why no mods? I'm sorry if I'm not supposed to have mods on but what is the reason for having no mods?