I've been working on building a "proper" etching tank for etching PCB's, with a heater and an air bubbler and all that.  One of the biggest challenges is getting a heater for it; aquarium heaters are the cheap, popular choice, but most have a max temperature adjustment range of around 85 degrees F, which is way too low for etching (ideally you'd want more like 115 F).  I just received a heater I bought online today, it's a Hagen Thermal Compact A-722, 50W 6" heater, and it's fully submersible (bought mine from petking.net for $9.99).  After some adjustment, I left it in a container of water for quite a few hours and it maintained the temperature at 115 F just fine, so I think it's going to work out quite well.

When I get my etching tank more complete, I'll put together a short article on it, in case anyone's interested.