It obviously depends a lot on what you're looking for and where you're located etc. Gnomon Watches (Japan) has a great selection and good prices, especially when it comes to Seiko. Just be aware that you don't get the GLOBAL warranty when you buy Seiko from Japan, but would have to send it back to Gnomon in case of any issues. 

James Porter & Sons is always a pleasure to deal with too. They have everything from Doxa to Grand Seiko and Oris. UK based. 

Never bought anything from Topper Jewelers, but they're always mentioned in the context of good online retailers. US based.

Just a few examples!

Anything with flat polished hands or bezels is a nightmare to shoot as they are practically mirrors. Block out the reflections completely and they go black, let em reflect light and you end up with a blown out crystal. Tricky to find a good middle road.

An example of an almost black polished bezel (after a few attempts to salvage it in lightroom 😂):

Me and the Mrs! 👌

Cut a hole in something black and shoot through the hole! This hole is obviously sized after my camera lens, but still! Blocks out all reflections! 

This should be recognizable across the street right?