This thread is 10 years old, but it's in the wiki so I'm bumping it anyway

I just used an eSIM from Tune Talk (an MVNO on Celcom's network) and it worked great. You can buy an eSIM with a plan online or in the app, and you can do the mandatory ID verification in the app. Allegedly it can validate your passport against a selfie automatically, but it didn't work for me and I had to opt for "manual verification" which the app says takes a couple days. I did it a few days in advance, so the SIM worked as soon as I landed.

The cheapest pack is RM 20 (~4.5 USD) for 10GB in a month. Coverage on Penang was good, speeds were 50 down, 40 up on LTE. A Malaysian or Singaporean phone number is required to set up the Touch-n-Go eWallet for QR payments and to reload TnG cards for road tolls from your phone, so it was definitely worth the extra setup time vs. using Airalo or the like.