Well excluding the 10 man Strat, Scholo and LBRS runs and the 15 man UBRS runs: Molten Core. We went in by forming a raid out of the 2 biggest guilds on the server at the time, along with some people who werent in either guild, but were picked for their ability and role (me being in the latter group). We spent about an hour organising the group, setting up pally blessings, organising mana drinks, healthstones etc. When we finally got started, we just wiped a lot on the first 5 trash packs and gave up.
I eventually joined one of the large guilds about 2 weeks later and downed Lucifron on the first night.