Welcome to Travelpod Chris!
Your previous trips sound really interesting! Riga sounds cool.
I've not been to Oz, but have been through Bangkok several times and Singapore a few. There's loads to do in both cities. I've always liked Bangkok and love it's colourful variety, though I do have to admit any more then a few days and I'm ready to head out for some clean air!

It's pretty easy to get around, there are loads of good places to stay and
lots to bide your time with. The food is great and there are lots of interesting characters to meet.
Is there anything in particular you want to know? Or see?