love the washing machine idea!!
DS is 5m and I'm finding it much harder work keeping him entertained as developmentally he's had a bit of a leap of late and needs so much more. In particular he loves objects so I spend a lot of time trying to (1) find objects that are safe (the unsafe ones always seem to attract him like a magnet, garhh) and (2) put them somewhere he can reach them (he hates being helped so I have to convince him he's done it himself!!).
His chief activities are:
songs/rhymes
looking at books
holding/eating/scragging various objects (see above)
watching me put the washing out/bring it in/water the plants/make dinner
me carrying him about the house to look at pictures, photographs, plants etc
me holding him up to the mirror and saying hello baby BOO!
me holding him up to look at the clock and saying tick, tock, tick, tock with him
peekaboo
With the weather so hot I'll also sometimes take some cool-ish water out into the garden in his old baby bath (he is too big now so we use the family bath) and give him a mini splash about.
Once his daddy is home there's a bit more energetic play/tickling/holding up in the air etc. I'm usually too knackered!
You could also try baby massage if you have classes near you?