I've read that the deep Thai mortars are best. Any sources?
Any sturdy, deep, big, stone mortar and pestle is a great choice! There are dozens of cultures that use them; the styles may differ slightly, but the important thing is the quality of the material and the size that you want.
Most any that look sturdy and are heavy for their size is good. I prefer to use a molcajete as a mortar and pestle as it will season over time and make your food taste better and better.
If you have a Chinatown near you, go there. It'll be significantly cheaper (and most likely better) than anything that Williams-Sonoma or the like has for you.
And pay attention to the graininess of the mortar/pestle - some of the marble ones are so smooth that the spices just move around without being crushed. The act of using a mortar and pestle involves both pounding and crushing but a slightly roughed or grooved surface helps get that going. (Note this is only slightly - it's not going to feel like sandpaper but you don't want it super-smooth).
Make sure it's big enough, the tiny ones are basically useless.
I'd have a look at something like this:
That's the same type I have. Cheap..about 15 bucks at the local Asian store. I'd bet shipping for that heavy thing is wild tho.
I also used it to pound chicken breasts flat sometimes. Between wax paper and using the bottom of it as the impact point..but the bottom bit is a rough and textured so it's not all that great for that but works and will tear the paper. I have a proper 'pounder' now.
I would LOVE to have a molcajete. That's what I'd recommend. Get the biggest one you can fir on your counter and let it live there.
I inherited a big brass one from my great aunt. It's very deep and has a powerful pestle, so it works really well, but if I were buying, it would surely be a molcajete.
Here's a link to the last time the Hotline discussed this ever-interesting topic: