Are you level 60 yet?
If you're not, then save up for these:
Don't spend gold on gear if you're not level 60, you'll replace whatever you buy along the way.
If you're level 60:
Regardless of level, are you interested in professions? Then use the gold to get the recipes and level your profession up.
Other than that, there's a lot of stuff to spend your gold in. Appearances, toys, mounts, pets, old world recipes.