What are your best and worst purchases when it comes to cleaning?
For me, my best was my Karcher. It has literally changed my life (saddo). Takes me 10 minutes to do my patio doors inside and out. They used to be the bane of my life as the sun shines on them almost all day after midday, so I would clean them, think they were clean and then the sun would pop over and the smears 
would appear. Now if I could just somehow teach the dog to stop dribbling and snotting up them so they could stay clean for longer than 10 minutes at a time 
Another, while not exactly a gadget as such, was a long handled scrubbing brush (Oxo one, from Amazon). Marvellous! I scrubbed all the tops of my kitchen cupboards (the bit above, like a coving type thing?) with very little effort. I'm all about maximum results for minimal effort where possible!
The worst was the steam cleaner. 3 of the bastards. All crap. All a massive faff to use. A mop and bucket is so much quicker.