I have a friend who always uses gingernut biscuits for her ripple cake - she reckons it's great.

Other variations I use and/or know of:
- butternut snaps with crushed crunchie in cream
- choc biscuits with sprinkle of peppermint essence and crushed peppermint crisp in cream
- choc biscuits, sprinkle of alcohol on biscuits (ie, cointreau) with chopped strawberries in cream
- and I haven't made it, but I've seen a recipe for "black forest ripple" - choc biscuits, a dash of alcohol on biscuits (rum?), chopped black cherries in cream plus cherries and choc for top of ripple cake.

Whatever you use it's all yum, yum, yum!