man, there are so many good ones!
Tyrant- +1 T bigname, reroll successful wounds on your guy helm + IF, HA and either a GW, or just handweap + potion of speed means you have a monster in combat who is either ASL, but hits a lot and like a truck, or str 5, but with that nice Init + the pot for I7 for a turn. both styles are resiliant.
Also, there's the classic WS10 sword + -1 to hit you armor. throw in a CoC, and you have a solid lord right there.
Slaughtermaster: This guy is usually my general and I find my chars not dying so much to being attacked, but from being overrun after a combat goes particularly bad for me (usually not hitting with even close to 50% of my attacks). Therefor, I think a CoC is CRUCIAL for any army. If nothing else, this guy will have that. If I have the points, hellheart is nice, or if you use an ogre hoard + a smaller unit, you can start off in the smaller unit, use grull's sickle and just run to big unit when danger approaches (to save wounds on the money unit). units with a frontage of 3 containing a FC can also protect your casters by putting the characters in the 2nd rank and not making way, so protection is not AS vital as with most casters. So that's something to consider, but grut's sickle coupled with a successful gut mgc cast and blood gruel means +7 to cast on most of your spells each turn! I cannot stress how many dice this can save you over each phase (AND cost your opponents in dispel dice!). It also increases the efficiency of a 3 wizard army substantially. That's worth the risk of rolling snake eyes, I'd say.
Butchers: Pretty standard, really. Give em a great weap and stick em in the 2nd rank of a unit if taking anything other than gut mgc. Wider frontage and putting him in front is acceptable if he has gut mgc and is able to get wounds bck. Dispel scroll is nice + so is the channeling staff. The forsaken rod is awesome on one of these guys coupled with gut mgc to redeem the lost wounds. ESPECIALLY if your SM has gruts sickle and you'll get those extra dice you don't need with him to increase the chance of successfully casting the L2's spell to get his wounds back. Sometimes a feedback scroll coupled with sniping maneaters can really ruin an enemy character's day.
Speaking of Maneaters: give them a brace of pistols, sniping and one of the other rules and a flaming banner and you have a delicious wizard/other character killing or regen hunting unit. a small unit of these guys inflicting a single wound and all those other units with shooting can unload into the targetted unit and reduce them to gore in a single shooting phase. If you haven't tried leadbelchers yet, run a couple units of 5 with a bellower, or even a big unit of 10 with a bellower to put some serious pain into an enemy unit every turn while backing up as they advance, then rank up to recieve a charge. They can still beat many of the common rank n files in combat!
Firebellies: same as the butcher (minus the forbidden rod), except it might be more practical to stick him in the front rank with his flaming impact hits on the charge. Otherwise, just keep him in the 2nd rank. A potion of speed is awesome with this guy if you're virtually guaranteed a charge for the I5 breath weap attack. Remember, this is a special close combat attack and so if he's in the back rank he'd only get 2x other supporting attacks when he uses it.