If you want to be quiet about it, gold is pretty good - no-one will be massively surprised if you turn up wanting to sell gold, whereas ruthenium would be another matter... However, if you're planning on making anything like gold, silver, platinum, etc., making a lot and putting it on the market will risk devalueing it - so maybe don't go too mad churning out ingots of the stuff.
Synthesising rare elements could probably get the attention (and funding) of various laboratories worldwide. However, it would definitely begin to draw notice if loads more osmium appears in the world, for example, which might not be as helpful if you want to keep it secret.
If you're willing to stretch past just elements, and be able to control the crystalline/molecular structures of your creations, then that could go well. Everything from proteins for crystallography (that no-one can grow in nanograms, i.e. cryptocromes, let alone 100g!), through to really really pure water - scientists would be really happy! Also, if you could control it to a high degree of specificity, perhaps manipulating just a single amino acid, then guaranteeing purity would be an amazing base for research. (I'm talking millions/billions of dollars of research).
If you can create a molecule as you wish, purity is an incredible thing scientifically - but even knowing what impurities you've included would be a godsend. You'd need to be public about it, because no-one would really take you seriously if you just turned up at a lab with a sample, but you'd earn one hell of a lot of money once you got credentials and confirmation. You might not be able to make drugs for the whole world, but you could progress research by huge leaps. (Medicine, engineering, photovoltaic cells... So many diverse disciplines could benefit from it!)
Also, if you're the only one who can operate this philosopher's stone, you'd probably want protection from a government/global institution - you'd effectively become a single-person superpower with such an ability. While aligning with any institution would give them power too, you'd also get a decent benefit yourself (by not having a really easy target on your head).