So as the title says what is your Assassin/race combination? Personaly I had Nord assassin type character. But lately I decied to try out Dark elf~ pure dagger assassin build.
I'm not sure if it's good race for a melee assassin, but I'm not really fan of Khajiit race (only reason I would pick Khajiit is for the sake of having better sight during night).

Orc, with warhammers

Argonian, Khajiit, Bosmer, and Dunmer make great Assassins...but i use Breton just because i can

My assassin character is an Imperial Necromancer who has been driven out of his homeland of Cyrodiil.
He had been preying on unsuspecting travelers, bandits, merchants, stray adventurers etc. for decades to perform
dark necromantic rituals in order to prolong his life.
One day he had taken a child whom he thought was a runaway, but who was in fact a lord's only son,
and it didn't take long before the lord's men stumpled upon the Necromancer's lair. He had to flee the land, but was caught
by the Imperial Legion on his way to Skyrim. He joined the Stormcloaks, since he thought that a land without the Legion to
protect its citizens would definitely be easier to navigate as a Necromancer. He couldn't care less for Ulfric or the Nords.
Soon after his arrival in Skyrim, he was contacted by the Dark Brotherhood and there he found someone who truly understood
him.

I started a high elf character and decided to go the stealth-magic route with it. Personally though I think that bosmers are well suited due to their affinity with the archery and alchemy skills.

Khajiit would also be good but seem more inclined towards thievery. Then again, night eye would be damn handy for any assassin...

I'll use a Dunmer always as my first choice.

Sometimes just to mix things up, I'll use a Khajiit simply because they're good at it and I like the kitties.

When I end up trying out assassin builds, I usually go either Wood Elf, Argonian, or Khajiit.

Wood Elves for the archery bonuses, Argonians because I think Argonians are awesome, and Khajiit for the previously mentioned night sight.

I just finished my first Dark Brotherhood playthrough with a pure ranger Bosmer.
I'm now trying a pure illusionist Dunmer.

Khajiit, out of vanilla races. With modded ones you can't go wrong with Moonshadow Elves

Well according to lore, Argonians are good assassins and are immediately given to the dark brotherhood if they are born under the sign of the shadow.

I use an Altmer assassin primarily. Daggers, invisibility, & paralyze. I can get around the battlefield so fast it looks like I'm teleporting almost.

I made my assassin a Bosmer as it was my first assassin in Oblivion and my second was an Argonian. If I had to choose a second race for an assassin, I'd probably make an Argonian and I'd role-play him as a Shadowscale. I'd try a Khajiit but I've never tried that race before. I might also try Dunmer for an assassin, but I'd rather be a stealthy spellsword instead.

Bosmer. Since Morrowind I always play a Bosmer sneaky char first.

Bosmer...u can eat the evidence:)

Imperial assassin for me.I prefer the human races.

Only assassin I have had was Altmer. He was actually a Thalmor agent and used DB only as a tool when he committed several political murders all around Skyrim.

Like alot of races Bosmer, Dunmer, Argonian, Nord, Breton. but my fave for assassin is dark elf i may try out that moonshadow elves mod

I've gone for a completely different style of assassin to the normal stealth / dagger / bow.

I've gone for a Dunmer stealth / illusion / destruction style mage assassin. I did this to get Dunmer lore of being connected to the Daedric Prince Boethiah and also them starting assassin guilds such as the Morag Tong and the Dark Brotherhood and then to mix it with them being the master race on destruction.

I am just about to experiment with using runes as a way of assassinating contracts.

I have no set race choice for assassins myself. I might make a Dunmer Assassin soon though.