Utterly Mad

If I were to host a Minecraft Server, what mods/plugins would anyone want?

Edit: Also, after roughly checking the electricity cost, it'll cost me £12/$16 per month to run the server 24/7. So it may be an option to have it 24/7 if required, but I'll likely just end up running it for 12 hours a day instead, since we're all in fairly close timezones.