Photo of the rockery please! Which direction does it face, ie does it get sun most of the day?

And how big is it, is it shaded by trees or shrubbery?

Something to consider is how long a lease you have - you don't want to invest heavily in something that you might not get to enjoy.
You could plant spring bulbs for starters - iris reticulata and mini daffs/narcissus. Heathers are relatively cheap (I got some for £1.25 a couple of weeks ago). You may also get small alpines (3 inch pots) that you can cram in between the stones.

Following Urbanite's theme: crocus, snowdrops, lobelia, lots of saxifrages, thyme, dryas, sempervariums, sedums...

If you are planting Heathers Debbie, put them in their
own patch of Ericaceous compost.
I have also just discovered Gentians should be in lime
free compost. No wonder mine died in the planter, we
all live and learn.

As an aside - I picked up a basket of 6 Autumn heathers in Aldi for £3.99 yesterday - some with interesting foliage and because they are in individual pots you can mix and match the ones you want!

That's interesting Diane. One of my garden encyclopedias says add a little lime in the form of dolomite and the other says neutral to acid soil! (I looked it up because I've just been given a gentian and never had one before)Google says 5.5 -7. So I'll ignore the lime but not use ericaceous compost as we are 6.5 here. Doesn't look as if that was the cause of your gentians dying - what a shame.
(Sorry to get off your subject Debbie)