I think you could plant any shrubs or herbaceous plants really, especially if it's growing in a pot, because you won't be disturbing the roots.
If you're moving an already established plant growing in the ground, maybe it would best be left until the autumn.

Make sure you give whatever you plant plenty of water. The ground can dry out quickly in August, even after heavy rain.

Some seeds could be sewn at the end of the month - I like to sew Sweet Peas, and things that will flower in the spring (Forgetmenots, Aquilegias, Bellis etc) .... but I don't sew them directly into the ground. I like to give them some protection in the winter, so I sew them in little pots or seed trays ... and plant them outside in the spring.

Maybe you'd also be able to buy some spring flowering bulbs later in the month, and they can be planted out as soon as you buy them.

Hardy biennials would do too, like 'sweet williams'
But as Hywel says pot grown shrubs will do well,
I think you should look at some of the beds and borders photos on Goy, shoving any old plant in could cause problems in the future for you when a pretty little shrub gets its roots down and turns into a huge thug. :0)

a wee bit of thought to size, colour etc....and don't forget all the lovely spring bulbs available in the shops soon