Good option for Singapore (and possibly surrounding countries) - eight - https://www.eight.com.sg

After being let down by Singtel's tourist eSIM on a trip last month (worked fine in Singapore, but not in Thailand despite including roaming there), I decided to try out one of the Singapore MVNO's. eight is owned by StarHub, have online signup for an eSIM (need to 'scan' your passport, but that's required for all SG SIMs), and for S$8 (US$6) you get 288GB of data in Singapore, 10GB of "APAC roaming" (which only includes abut 6 countries, although interestingly one of them is India) and 2GB of roaming to other countries, all within 30 days. You do need to be in Singapore to activate the eSIM, so the roaming won't work if you're not going to SG first. No voice/SMS options for non-SG citizens/residents. You can also get a SiM card if you prefer, but whilst there's a number of locations to pick them up, none are really convenient to tourists (eg, none at the airport, although there are options at the Somerset and Promenade MRT stations)

I purchased before I left home, activated the eSIM on transit in Singapore, then used it in Malaysia for a few days before returning to Singapore for a few more days. Worked great in both countries. Not sure if I'll be travelling internationally within the next ~22 days, but if I do then having 2GB of data for that trip will be a nice bonus too!