You know, you sort of neuter the question right off by saying not to include Trips, Cena, and Batista, as I feel those are the three putting on the most boring main events. Let's look at the other guys:
Randy Orton: He doesn't get lumped in for the simple fact that...well...it's not his fault. There have been absolutely ZERO new main eventers made for the RAW brand since...well, Batista. We're talking FIVE years with NO new stars. Orton is the defacto #1 heel on RAW...and he's the ONLY main event HEEL on RAW (until Big Show is done having his cup of coffee with the Tag titles). So, naturally, his schtick is gonna seem old and boring...but he's had to fight the same old, boring match now for nearly five years. Orton has, at least, added dynamics to his character, such as the addition of Legacy and his increasing chickenshit antics. His offense, which slightly boring, at least has realism added to it, unlike the Superman offense of Cena and Trips.
Undertaker: He's capable of good matches with everyone and is constantly changing his arsenal of moves...he also put on one of the greatest Wrestlemania matches in history...at 46. The guy is the complete opposite of boring, as each appearance commands attention.
Chris Jericho: Probably the best all-around gifted heel since Ric Flair...never boring, even when saddled with a useless tag partner (Big Show) against a so-so talent (MVP) and another worthless tag partner (Mark Henry). Granted, Jericho and MVP have been carrying the feud, but it's Jericho's solid work also on the mic that's been putting this feud over. Plus, he's putting on fantastic singles matches to boot. The cure for the common boredom is Chris Jericho.
CM Punk: If you say he's boring, especially after the awesome program with Jeff and the great work he's been doing so far with Taker, you must be high or ******ed. If it was a year ago with babyface Punk...maybe. But heel Punk is taking Mr. Chicago Made to a whole other level, one we haven't seen since his heel days in Ring of Honor.
Christian: Yes, there's another brand, and they have "main eventers" too! Christian is consistently a Top 5 pop guy and has had great match after great match since coming back. Given, his character is lacking the same dynamic he had when he was a heel, but he's apparently comfortable in the smartass babyface role, especially when given such great heel detractors...
William Regal: This guy is absolutely amazing. His move to ECW has revitalized his career and will (hopefully) lead to his first major World title win on Sunday. The pairing of the silent Ebony & Ivory killsquad in Big Zeke and Kozlov give Regal even more reason to be a smug Brit, having two huge guys that got his back waiting in the wings in case there's trouble. Outside of Punk, this guy is up there as far as ME-level transitions go.
Who else? Well, you have guys just outside the bubble (MVP, Morrison, Shelton, Mattsy-Poo) and guys not around at the moment (Edge is injured, Jeffykins is taking a powder, Rey Rey is in Mexico crying in his steroids). This goes to show you the state of the main event on each show. While RAW only has one legit ME-level heel (Orton), it also has 3 babyfaces (Triple H, Cena, Batista), and that's BEFORE factoring in HBK. Smackdown, on the other hand, currently has 2 main eventers...that's right, two, and it's the guys fighting for the title. The third (Jericho) is wrapped up with the tag belts. ECW is the closest with a balanced main event, as Christian and Dreamer rep the babyfaces while Regal & Friends and Shelton make up the heels. It would be nice to see that kind of balance amoungst the other shows.
Can we just can the WWE talk and just say Matt Morgan is the most boring main eventer? He's so-so on the mic, so-so in the ring, and has a so-so look (kinda goony looking for his size), yet he's CONSTANTLY getting that main event push, mostly because Cornette loves him for whatever reason. It's taken two years already...it's not going to happen.