Achievement chests help a lot, as they give gold the higher you get. That does take a while though.
The wealthiest member of my guild got that way because she buys gems every month with real life money, which she then uses to buy Black Lion Chest keys. She gets valuable dyes which she then sells on the TP, and BL Tickets and Ticket Scraps she uses to buy weapon skins from the Weapon Specialist and sells those on the TP as well.
Keep in mind that it’s not just a matter of making gold, but also NOT SPENDING gold (or silver or copper) on travel. WP costs add up. Are you out at the edge of Tyria and want to go to LA? WP’ing to LA can cost 4 silver and change. Not much, really, unless you do it 10-20 times a day, and that really adds up fast. If you’re not in a hurry, go to the PvP lobby or WvW, then take the Asura gate to LA. That will save you some cash daily, and that adds up over time as well. If you havne’t unlocked the PvP lobby yet, take a few minutes and get it done.
Crafting mats, I think its been said here, are also a great way of making guild wars 2 gold. Since ascended crafting arrived, things like linen and silk have jumped in price. Are you selling your light armor pieces to the merchant? Shame! Salvaging them for the linen/cotton/silk may make you more cash. ALWAYS check the price of your blues and greens on the TP before you merch them. You’d be surprised to learn that lvl 50 blue cleric’s mace with a merch price of 50 copper can be unloaded to a buy order on the TP for 2 silver. Blue and green shields and maces always (well, ok, 95% of the time) sell for more on the TP than the merch price. Make sure you check your projected profit before clicking sell, as the TP takes slightly more than a 10% cut. Shaman gear and weapons seem to have nice prices as well, especially the weapons. While some rares have TP prices in the low 20 silver range, others will sell for 30+ silver. Check before you salvage for ectos!