An easy step-up from vinegar would be hydrochloric acid, $\ce{HCl}$. It's known as muriatic acid and is sold in bulk at pool-supply and home-improvement stores. The concentration from such sources is typically ~8.9M, or 32% (by mass). Such is what I measured from home; it's typically advertised as 30%-32%. There are rumors (which I haven't been able to confirm but suspect are true) that $\ce{HCl}$ from these sources often has iron contamination, but that is generally a minor concern for etching processes.
$\ce{HCl}$ has been widely used for etching aluminum hardware and paint-thinning in construction etc. It is highly reactive with (unoxidized) aluminum but can still etch other metals with more effort / more concentrated solution. You probably already know, but it's best practice to clean and polish a surface before etching, to remove impurities like oil and dirt, but also to expose the pure metal by removing protective oxides on the surface. The rougher the better (you can always polish-up later).
Brass is a simple alloy of $\ce{Cu}$ and $\ce{Zn}$. The reaction enthalpy of $\ce{Al + HCl}$ is -1,062.74 kJ, whereas that with $\ce{Zn}$ is only -153.90 kJ. Copper is hardly reactive with $\ce{HCl}$ alone, so it follows that $\ce{HCl}$ is a much stronger etchant for aluminum than for brass, although it is still possible to use it. There are many types of brass -- generally, the more $\ce{Zn}$, the better $\ce{HCl}$ will etch the material:
It is fine to dispose of $\ce{HCl}$ down the drain etc., but only do so after diluting it (carefully, slowly and substantially with water).
You can boost the performance of $\ce{HCl}$ as an enchant by introducing hydrogen peroxide, $\ce{H2O2}$. This combination has very strong oxidative effect and can dissolve metals like copper with ease. If you want to be environmentally friendly, this would be a good stopping point. The most powerful etchant will result from higher concentration of $\ce{H2O2}$. It's typically sold at 3% in stores but food-grade 30% $\ce{H2O2}$ can be bought online or made at home via this method.
I have had great success etching copper (and nickel) using a home-made solution of copper II chloride $\ce{CuCl2}$. Copper (I/II) chloride is very hazardous to aquatic life and (dissolved in solution or not) human life, but with careful handling it's a fine thing to use. It is quite easy to produce and handle, and does not corrode other (more precious) metals, like gold, so you can get selective etching if you have a certain alloy or something like RAM cards from PC parts. (I have isolated gold metal from these using $\ce{CuCl2}$ solution). To make it, simply add copper metal to a solution of concentrated $\ce{HCl}$ and very slowly add concentrated $\ce{H2O2}$. The copper metal will dissolve/oxidize into $\ce{Cu^{+2}}$, and if you dry the resulting blue-green solution (you don't have to) completely, you'll be left with a brown $\ce{CuCl2}$ powder. It's hygroscopic so if you leave it out it will form a blue hydrate. So I keep mine in a tightly closed plastic bottle. To use it as an etchant, just take some of the solid and dissolve it in water (again). The chief downside, as you mentioned, is the toxicity of copper chloride -- I have never thrown mine away. You can re-use it many times.
If I ever had to dispose of it, to do so properly I would use electrolysis. Attaching a DC power supply with the (-) terminal on a piece of copper metal (in dissolved $\ce{CuCl2}$ solution) and the (+) terminal in the solution (or attached to an iron nail) would do the trick, though you'd have to wait some time for the copper in solution to reduce -- and to push equilibrium you'd need a moderate/high voltage. Once you've reduced most or all of the aqueous copper to solid metal, the solution leftover is relatively harmless.
