So, as much as I play theme-park MMOs these days, I kinda hate them. I love the number of people they attract, and I have met some really great people in them (well, and some honestly awful people and players), but the games... bleh. I was probably "over" WoW's raiding game in Vanilla during Nax. It was fun, don't get me wrong, but some of the bosses were just starting to show me some limitations with raid-based content (mainly, that there's a gimick to the encounter, like in single player games, but unlike single player games, MMOs require you to repeat the task for months at a time). I still play theme-parks, but I try to do things differently than your average player.
Economic pvp is one of my favorites when I have the time and, especially, access to the trade skills. The idea's real simple: find a fairly solid market and take control of it. There's a lot of ways to do this, such as buying up that market and relisting it for a profit, or massively undercutting the market and buying out your opponents until the market obeys your undercut, then massively increasing the price again to make the profits, etc. Huge gambles, angry tells, virtual tears, etc. It was the most satisfying thing I got out of Horizons, which was largely a pve game since you could not physically attack other players, and it really helped me perfect the art since it was a player driven economy. I did it on a WoW server as well (well, a few), and it made me a lot of cash, but felt more hollow, since WoW's just... so big. It's much easier to get away with it since there's so many niche markets, so people worried about angry tells probably don't have to worry about this as much, especially if you post on a bank alt.
Player run events are another thing you can do. I know, theme-parks don't always give the best options for this. For example, Darkfall Online has a lot objects, items, and a player-base for this sort of thing. Game Masters can also give special itms for in game events, and may advertise them officially. Horizons did the same, and I even remember when a GM showed up and (it was a roleplay story telling event) took screenshots, including when I called him a "mucker." WoW... does not do this. However, it's still something you can pull off non-officially. Generally, center it around something people already do in a busy area, and if it's going to be affected by a patch, even better! For example, the day before the Dalaran portals were to disappear, my guild arranged a "good-bye to Dalaran" event since folks were obviously going to move out of the former capital city. We posted the information on the server forums, let people know in trade chat, and just got people together and used a lot of fun and holiday event items (reindeer mount transformations, booze, laser-pointers, forced player transformations, booze...). It was pretty fun. You can also do things like nub races, weddings, role-play events... just remember who the audience is and ask yourself how the event can be messed up, such as in a pvp event.
PvP events in a theme-park game can be the easiest event to set-up, but also the hardest. Unlike in games with FFA PvP (like Darkfall), offending players can't just be ganked to hell to keep order. You need to control attendance at times, since massively uneven sides aren't fun. This is even more important if the event's more than a glorified king of the hill match. If there are specifal rules, such as "no flying mounts," you can't simply invite everyone and anyone, since people with flying mounts can simply go to a high point and perch event goers. RP events have a similar situation, in that anti_RPers on "your side" can't simply be removed. You need to invite people carefully (probably on an individual or guild level) , and KISS- Keep It Simple, Stupid ;P. The more complex the event is, the easier it is to ruin or have things go wrong. If it's cross faction and there are language limitations, make sure you have some external communication available to keep communication going before, during, and after the event. Forums, Voice chat, Real ID for WoW, etc. Communicate often to help avoid drama!
Finally, self imposed gameplay options! Only level through gathering or pvp, level naked, only in enemy territory, etc. Slowing down the grind and doing it in a unique way can make the game a lot more fun than the simple grind, especially if you know end game isn't something that interests you.