In reply to katyc:
We were there lately, Grindelwald is difficult for free parking. Think the cheapest is over the river by the Grund station (6 francs per day), otherwise you can try driving up the little roads beside the ski piste or there's a layby on the hairpins up towards Isenfluh (nr Lauterbrunnen), I've no idea if you'd be moved on.
There will be places towards Interlaken I'm sure as HeMa has suggested.