If you're trying to decide which professions to put on your character and you are considering their gold making potential, you'll want to avoid engineering and inscription. While they're not terrible if you consider their stat bonuses, they're not ideal for gold making on many realms.
Of course, every realm has its own ecosystem, and as with all advice you'll read from this column, you should check that the assumptions hold for your realm and faction. That said, by far the most common problems I have trouble helping people with are related to these two professions.
I'll start with the one that's going to get me the angry comments first. Inscription has long been touted as a cornerstone of the money making meta game -- heck, it earned my esteemed colleague, Fox, his first million gold on Darkmoon Cards. Before that, we had "glyphsmas" when 4.0 hit and a steady level of demand for glyphs before that. We still have the stupidly profitable fortune card market that lets anyone open a tiny, Blizzard-sanctioned casino. So what's not to like?