I'm using the dennerle corner filter on my P@H 27l. Was pretty chuffed with it at first but it's starting to wind me up. Positives are (removable) spray bar, adjustable flow. Negatives are stupid sponge it comes with (which I've chucked out and replaced with siporax but was/is a pain) and the fact that it's designed to come apart on you when you try to lift it.
I think this is deliberate as I think it's made so that you just pull off the front panel and take out the internal sponge, rinse and put back in. Not so good when you've changed to proper filter media.
Heater - I'm using the aquael neo heater. Really good piece of kit, so impressed with it I bought a bigger size for my main tank. Electronic setting and saves having a thermometer as it has one integrated. Very thin and discrete too.
Have tried a couple of LED lights but wasnt' happy with either so back on the P@H supplied one. It's ok, just not that attractive but I don't want strong light on my nano so I'll probably make do. Hopefully Phil will see this and comment, I know he's been on the search for nano lights and has done a lot of research.