Their names always take the form of two words which can be linked with "and" to form an idiom. The split cards printed as of July 2014 are:
Invasion: Stand // Deliver, Spite // Malice, Pain // Suffering, Assault // Battery, Wax // Wane Apocalypse: Order // Chaos, Illusion // Reality, Night // Day, Fire // Ice, Life // Death Dissension: Trial // Error, Rise // Fall, Hit // Run, Pure // Simple, Supply // Demand, Crime // Punishment, Odds // Ends, Bound // Determined, Hide // Seek, Research // Development Planar Chaos: Dead // Gone, Rough // Tumble, Boom // Bust Dragon's Maze: Protect // Serve, Far // Away, Toil // Trouble, Armed // Dangerous, Alive // Well, Profit // Loss, Turn // Burn, Down // Dirty, Wear // Tear, Give // Take, Ready // Willing, Beck // Call, Breaking // Entering, Catch // Release, Flesh // Blood Other:[Who // What // When // Where // Why], [Naughty // Nice]
Naturally, one of the challenges in designing split cards is simply coming up with "X and Y" word-pairs that are both a recognised phrase or idiom, and also words that can at least faintly plausibly be names of Magic cards. AlexChurchill put together a list of such idioms, collected from a few places. The list is below.
The list is in two parts: first phrases from general usage; and then specific names of relatively well-known works of fiction or similar.
Above & Beyond Agony & Ecstasy Air & Space All & Sundry Arm & Leg Bark & Bite Beer & Skittles, Beer & Pretzels Bells & Whistles Better & Worse Birds & Bees Block & Tackle Blood & Guts Born & Bred Bow & Scrape Bread & Butter Bits & Pieces Bright-Eyed & Bushy-Tailed Bubble & Squeak Cash & Carry Cat & Mouse Cats & Dogs Chapter & Verse Checks & Balances (clash with MTG: Checks and Balances) Cloak & Dagger (clash with MTG: Cloak and Dagger) Crash & Burn (clash with *both* MTG: Crash *and* Turn & Burn) Cross My Heart & Hope To Die Cut & Dried Cut & Thrust Damn & Blast Dark & Stormy Day & Age (clash with Night & Day) Dead & Buried (clash with Dead & Gone) Devil & Deep Blue Sea Done & Dusted Doom & Gloom (clash with MTG: Gloom) Down & Out (clash with Down & Dirty) Duck & Cover Fair & Square Far & Wide (clash with Far & Away) Fast & Loose Fast & Furious Fire & Forget (clash with *both* Fire & Ice *and* MTG: Forget) Fire & Rescue (clash with *both* Fire & Ice *and* MTG: Rescue) Fits & Starts Fly & Game Fool & His Money Footloose & Fancy Free Forever & A Day Forgive & Forget (clash with MTG: Forget) Friends & Family Fun & Games Genius & Insanity Growth & Decay Guns & Roses Hammer & Sickle Hammer & Tongs Hand & Foot Hare & Hounds Have Your Cake & Eat It Head & Shoulders Heads & Tails Heart & Soul Heaven & Earth Hell & Back Here & Now Here & There High & Dry High & Mighty Hit & Miss (clash with Hit & Run) Home & Dry Home & Hosed Hope & Faith Horse & Cart, Horse & Carriage Hot & Bothered Hot & Cold House & Home Hunt & Peck Hustle & Bustle In & Out, Ins & Outs In One Ear & Out The Other Inside & Out Intents & Purposes Kicking & Screaming King & Country Kiss & Make Up Kit & Caboodle Law & Order (clash with Order & Chaos) Lean & Mean Leaps & Bounds (clash with Bound & Determined) Life & Limb (clash with MTG: Life and Limb) The Lion & The Lamb Live & Learn Lock & Key Loved & Lost Low & Behold Meat & Potatoes Meet & Greet Mice & Men Motherhood & Apple Pie Movers & Shakers Name & Shame New & Improved Nip & Tuck Now & Then Null & Void (clash with MTG: Void) Nuts & Bolts Park & Ride Peace & Quiet (clash with MTG: Peace and Quiet) Pins & Needles Once & For All Open & Shut, Open & Close Over & Above Over & Out Part & Parcel Power & Glory The Quick & The Dead Rank & File (clash with MTG: Rank and File) Rant & Rave Read It & Weep Rhyme & Reason Rich & Poor Rinse & Repeat Rise & Shine Roast & Ground Rock & Hard Place Rough & Ready (clash with Rough & Tumble) Safe & Sound Said & Done Shave & Haircut Short & Sweet Sickness & Health Sixes & Sevens Skin & Bones Slash & Burn (clash with Turn & Burn) Slings & Arrows Smoke & Mirrors (clash with MTG: Smoke) Snakes & Ladders Song & Dance Sword & Sorcery Stand Up & Be Counted Sticks & Stones Straight & Narrow Stuff & Nonsense Take It & Leave It Then & There There & Back Thick & Fast Thick & Thin Throw & Catch (clash with Catch & Release) Thunder & Lightning Time & Again Time & Tide (clash with MTG: Time and Tide) Tired & Emotional Tooth & Claw (clash with MTG: Tooth and Claw) Tooth & Nail (clash with MTG: Tooth and Nail) Touch & Go (clash with MTG: Touch and Go) Town & Gown Track & Field Tried & True Tried & Tested Twist & Shout Up & Coming Up & Down (clash with Down & Dirty) Up & Running Wake Up & Smell The Coffee Walk & Talk War & Peace Weights & Measures Well & Good, Well & Truly (clash with Alive & Well) Wheel & Deal (clash with MTG: Wheel and Deal) Wild & Woolly Wind & Rain
Works of fiction or similar: (Selected down to those where both elements are dictionary words, from lists such as http://tvtropes.org/pmwiki/pmwiki.php/Main/NameAndName ) Beauty & Beast Chip & Dale Dungeons & Dragons Ghost & Darkness (clash with MTG: Darkness) Ink & Steel The Goblin & The Grocer Jack & Beanstalk Magic & Mayhem Master & Commander Might & Magic Officer & Gentleman Pinky & the Brain Ratchet & Clank Sapphire & Steel Sonic & Tails Spice & Wolf Toads & Diamonds Will & Grace