DIY Terrariums - made from jam jars and planted up for Mother's Day
Tiny Succulents (eg from http://www.curiousplants.co.uk search for Sempervivum )
Layer the gravel, charcoal and compost in the jars.
Plant a succulent in the top.
Surround with small stones.
See http://brittanyanddylan.blogspot.co.uk/2011/11/weekend-project-1-terrariums-for.html for how they might look.