Killzone Mercenary & PlayStation All-Stars both had pretty sizeable patches, iirc (as in > 1GB)

Other stuff: Dragon's Crown; Rayman Legends; LittleBigPlanet.  No idea on the sizes of those I'm afraid.

Also, I think multiple games are being patched to support VitaTV, such as Ys: Memories of Celceta.

On a purely technical level it is now possible to own a Vita without a memory card thanks to Vita2000.  But I really wouldn't recommend it.

Vita TV pl0x.
Though if it means a cheaper Vita slim - why not. I already don't need much beyond the PSP 3000 screen, so...

Killzone got a 2 or 3 GB one, that was the biggest ever. But people complained and Guerrilla released a new patch that replaced the older one with around 800MB, that's what a new user would get. About 1 GB, it's not a good idea. If you will stay strictly retail and doesn't want to download a lot of demos, PS1, PSP games and so on, a 8 GB card is the recommended. A 4 GB could be enough, but I think the extra breathing space is worth it. If you plan to get a PS Plus subscription, then 32 GB+ is what you need. 

I only buy retails games, but I have a digital copy of PSABR that came with the console and I have PS Plus games (around 7 full games, 4 PSN titles, 1 PS1, 2 PSP games) and my 32 GB card is at 50%.

Dragon's Crown: only 23 MB

Rayman Legends: 389 MB

LittleBigPlanet: 334 MB (varies on the installed add-ons)

Ridge Racer: 930 MB (varies on the installedtracks, cars and music)

I'm sure the slim in the west would boast sales a lot.

I heard the patch for Killzone was reduced in size since though.

That's true, forgot about that.  My copy of Killzone has a 362MB patch at the moment.

Also, for completion's sake, here's how much all of my retail games take up on my memory card in case KHF was interested:

Dynasty Warriors Next - 0

Gravity Rush - 3040KB (includes DLC)

LEGO Legends of Chima - 0

LittleBigPlanet - 240MB (no DLC)

Need For Speed - 16MB

New Little King's Story - 3904KB (no DLC)

Ridge Racer - 801MB (all DLC tracks and most of the DLC cars)

Tearaway - 31MB

Uncharted Golden Abyss - 101MB (no DLC)

The Vita TV would be a smarter reveal right now, that will probably excite people more than a slightly slimmer model.