Icy Touch/Plague Strike
Your two openers combined into a single button. I also suggest keeping Plague Strike somewhere handy on your bar in case it misses for whatever reason or you need to refresh one but not the other. I keep this macro on my 1 key and Plaque Strike alone on my F1 key. I don't have to hit it often, but I find it convenient. Right clicking or holding a modifier will always cast Icy Touch for situations where you need to stay ranged, but still want to hit something. My death knight is also an engineer so I use my glove enchant every chance I get in macros rather than actually remembering to use it, but only in my DPS spec; I use my mitigation glove enchant when tanking more carefully.
/use [btn:2][mod] Icy Touch
/castsequence [btn:1,nomod] reset=5 Icy Touch, Plague Strike
/use [spec:2] 10
Death knights have a ton of abilities, many of which are pretty situational, like outbreak. It's not something that you use all the time, but is really handy in a pinch. I ended up hiding it behind pestilence because it made the most sense to me. I often hit my pestilence key with a modifier to apply diseases and then let go of the modifier and hit it again to spread them. It's great for getting aggro quickly on an AOE group.
/use [btn:2][mod] Outbreak; Pestilence
Chains of Ice/Festering Strike
Festering strike is another ability which is highly situational. In fact I doubt anyone not PVPing would even miss it if it disappeared tomorrow. It is accessible by using a modifier with or right clicking chains of ice by using this macro. Makes sense considering that it extends chains of ice among other things.
/use [btn:2][mod] Festering Strike; Chains of Ice
Communication is important when it comes to resurrecting, especially during battle. Also helps to announce when mass resurrection is being used so people don't try to run back. The following macro uses raise ally in combat and out of combat it uses the gnomish army knife or mass resurrection with a right click. In addition a customize message for each thanks to some LUA magic.
/use [combat] Raise Ally;[btn:2] Mass Resurrection; Gnomish Army Knife
/run p=SecureCmdOptionParse SendChatMessage('I am '..p("[btn:1,nocombat]defibrillating;raising")..' '..p("[btn:2,nocombat]everyone!;[noexists][nodead]someone nearby.;%t!"))
For non-engineers this would be:
/use [combat] Raise Ally; Mass Resurrection
/run SendChatMessage('I am raising '..SecureCmdOptionParse("[nocombat]everyone!;[noexists][nodead]someone nearby.;%t!"))
Darkflight/Path of Frost
This is sort of worgen specific and sort of not, you can replace darkflight with the utility ability of your choosing. When mounted or swimming path of frost is use otherwise darkflight. Using a modifier will cause the opposite ability to be used.
/use [mounted,nomod][swimming,nomod][nomounted,noswimming,mod] Path of Frost; Darkflight
Frost Strike/Death Coil
For frost death coil isn't ever use except on the off chance you need to hit something from ranged. This macro does just that by casting death coil when using frost strike while holding a modifier key down.
/use [mod] Death Coil; Frost Strike
Similarly for frost death strike isn't really used aside from self healing as needed. So this macro allows you to death strike using your obliterate key with a modifier.
/cast [mod] Death Strike; Obliterate
Bone Shield/Icebound Fortitude
Now for a tanking one. This macro only allows icebound fortitude to be use in combat so it isn't possible to accidentally burn a mitigation cooldown when it won't be used. This is also where I use my engineering mitigation glove enchant, but again only in combat.
/use [nocombat][btn:2][mod] Bone Shield; Icebound Fortitude
/use [combat] 10
When under the effects of the lichborne buff you become undead and can therefore heal yourself with your own Death Coils should you choose. This macro allows you to spam death coils onto yourself after hitting lichborne all with the same button. That's a lot of death coils! I added one for each second of the lichborne buff in case by some freak of nature you manage to get that many off and besides it's not like it hurts to have them there.
/castsequence [@player] reset=12 Lichborne, Death Coil, Death Coil, Death Coil, Death Coil, Death Coil, Death Coil, Death Coil, Death Coil, Death Coil, Death Coil
Ghoul Health Pot
Some death knights keep ghouls around for pets, I don't much care for ghouls and prefer to use them as two minute health potions. Hit it once to summon a ghoul and a second time to sacrifice your ghoul for a health boost. There is a two minute timer on your ghoul without talents so if you don't sacrifice it in that time then the button resets to summon a ghoul again.
/castsequence reset=120 Raise Dead, Death Pact
Hearth/Death Gate/Have Group, Will Travel/Dimensional Ripper/Wormhole Generator
Click to use hearthstone or right click to open a death gate. When in a group right clicking will summon your group/raid unless you hold a modifier key to open a death gate as if you weren't in a group. As added bonus holding down one of the three modifier keys will use a different engineering teleportation device.
/use [btn:2,group,nomod] Have Group, Will Travel; [btn:2] Death Gate; [mod:alt] Wormhole Generator: Northrend; [mod:ctrl] Dimensional Ripper - Everlook; [mod:shift] Dimensional Ripper - Area 52; Hearthstone
For you non-engineers this would be:
/use [btn:2,group,nomod] Have Group, Will Travel; [btn:2] Death Gate; Hearthstone
I'll include my mount macro here since my worgen death knight varies from all my other toons in that I have two ground mount possibilities I like to use. Using a modifier while swimming with use the seahorse, otherwise the deathcharger. Aside from that clicking will summon a flying mount when possible and revert to a ground mount. Right clicking will use a ground mount no matter what.
/cast [mod,swimming] Abyssal Seahorse; [mod] Acherus Deathcharger; [flyable,btn:1] Winged Steed of the Ebon Blade; Running Wild