I am thinking of things like - plants you've picked on a whim which have turned out to be fab, ones you thought wouldn't "work" which then surprised you, or ones which have given especially good "plant value".
The one that made me start thinking about this was a Knautia I got somewhere last year - totally unplanned & I didn't know much about them.
It didn't do much at all last year and I wondered if it was going to die... but this year it has grown beautifully bushy and been covered in flowers for MONTHS so I am very with it.
I also love my Bellis as they seem to flower all through the Winter and most of the rest of the year too (though they are looking a bit stressed at the moment, hope they will be OK), and the heucheras are fab too as they always look great and don't need any attention.
Very new to gardening, so currently, anything that hasn't died has given me great satisfaction! Probably very amateur to all you pros, but success stories this year have been lemon balm, lavender and rosemary cuttings, gladioli, courgettes and a castor oil plant.
My award would have to go to the aspidistra, used as garden plant.
I started with mere 2/3 leaf plants at $1 from Sunday markets in late 2006 and by 2011 had 14 huge pots crammed with luscious asps. Looking at the current silly prices, each pot is worth about $200. I've sold none of them, but used them as underplanting in our garden. I still have 5 pots left, now to be divided to make 10.
I know this is not about money, but value as the plant itself, its beauty; aspidistras were a stalwart of Aussie gardens back in the day, but fell out of favour. How wrong they are to ignore this lovely plant, especially the variegated.
I especially love the way, so far from being the precious plants that should be divided with extreme care in the UK, can be hacked up with a big spade, stuffed into the ground, watered, and stand back.
It all depends on your soil and site in your garden. My favourite climbing roses, of which I have 8 on 4 arches, is a german Kordes Rose, which I and neighbour had while living in Germany. It is bushy, slower growing than others with a large bouquet of very filled pink roses on each stem. Called ROSARIUM UETERSEN. Can also be pruned into a 6foot bush rose. Depending on the weather it will bloom in May or June for 2 months, and then blooms again after 2-3 weeks break. In this country I could get them only from C&K Jones . Bought 2 for my daughter, and doesn't even dead head them or fertilise them and always are lovely. Another climbing rose i have been able to grow in a pot is called Maid of Kent, lots of pale pink thin drooping stems . giving a waterfall of blooms effect