Pre-paid Data Everywhere

Nepal

Ncell 1GB for 30 days at 1000 Nepali Rupee (~10 USD) 300 Rupee for the Sim Card, 700 Rupee for the 1GB Recharge. More info, could be found at http://www.ncell.com.np/

Taiwan

Taiwan Mobile. NTD 100 for the sim card, and you'll have to top up another NTD 180 (~ USD 6) for the 1GB 30 days plan. The original NTD 100 in the sim card can be used for texting and calling.

Vietnam

You can buy a sim from either Mobifone/Vinaphone/Viettel. All of them have good coverage through out the country, even in rural area. They might not have micro/nano sim but they’ll be able to cut for you.

Unlimited data is available on all network for just about 3 USD per month but only available in high speed (i.e. 3G) for the first 600 MB. When you use over 600 MB, speed is limited but still enough for text/email/Google map. Data is not available upon buying the sim, you have to enable them. 

Vinaphone: MAX (to activate: SMS "DK MAX" to 888)

Mobifone: MIU (to activate: sms "DK MIU" to 999)

Viettel: MiMax (to activate: sms "3G on" to 161 then "Mimax" to 191)

USA

$2 per day plan from T-Mobile. http://prepaid-phones.t-mobile.com/prepaid-plans

Comes with unlimited voice, data and texts. Data is 2G though, but doesn't really matter for light browsing and Google maps.

If you are really need faster data, there's $3 plan which gives 4G LTE.

Malaysia

I haven't researched much, but bought a DiGi pre-paid sim which comes with data, in my first trip 3 years ago. Cost was like RM 25 -30.

Singapore

Also have few options to choose from, but I went with Singtel as it's the main provider. You will find the outlet when you exit the arrivals area (or just ask Airport's information desk).

There are few data plans and you can choose depending on the length of stay. I'd recommend the 1GB for $7 plan (valid for 7 days). Good enough for casual use.

Cambodia

I used Cellcard. Can be bought from the airport.The $4 card comes with 1.5GB of data. But you need to top-up another $5 to activate it.

They don't sell micro-sims. Had to cut a micro-sim from one of the phone shops in city. Also, for iPhone I had to configure the data network manually (guys at these shops knows the settings).

In Phnom Penh, most bars and cafes provide free-wifi and it's quite fast. So wait till you reach a cafe to upload the photos, etc.

Most road-side small shops sell re-charge scratch cards (usually $1 or $2). But they call it as Mobitel (not Cellcard).

more details: http://www.cellcard.com.kh/tourists-sim

Sri Lanka

There's at least 4 mobile operators selling pre-paid sims at the air port. But I'd recommend to go with Dialog cos they have better coverage in the island (I had 3G in the middle of a jungle to post a vine of baby elephants playing with each other).

Also, they sell micro-sims.

1GB - $10

512MB - $6

(more details here - http://www.dialog.lk/personal/international/inbound-roaming/tourist-plans/)

Australia

I bought a Ocpus from an airport kiosk which was a mistake. The package is $30 which includes a SIM and 500MB data + calls and text. It may be worth it for someone but it’s overkill for my 3-day transit.

New Zealand

I used Skinny: $5 (pre-paid SIM) + $10 (top-up).

I got to choose between Skinny and 2degree at the shop. Skinny provide cheaper and more flexible plans (weekly as well as monthly, data-only plans):

$4 - 200MB for 1 week

$16 - 500MB for 1 month + calls and txt

2degree only has a monthly package which costs $29 instead.