Go to the RHS website, select advice and then rabbit resistant plants - they have a list.

I had written an answer for you, then clicked on the RHS rabbit resistant plants page and my browser crashed! GRR

In my experience rabbits WILL eat Michaelmas daisies and Euphorbias.
I would add crocuses, snowdrops and daffodils to their list. Otherwise it's pretty comprehensive.

A friend's garden is absolutely overrun with the little blighters, and she finds that the young ones have a go at just about anything, and spit out the bits they don't like. Which is very annoying as the plant has still been cropped mercilessly even though it wasn't eaten.

A fence is the only answer.

Thank you to Bamboo and Beattie

I'm still trying out plants from the RHS website and find that some they suggest as rabbit proof are eaten by my bunnies.
Wild primroses, bluebells, daffodils, periwinkle, fuchsias are left untouched. Mint, ajuga, oregano, lavender and lemon balm seem OK and I'm trying out Indian mint - things with pungent leaves seem unattractive to them, but my thymes are being eaten. All dianthus species are eaten except Sweet Williams. Schizostylis and nerines are nice to look at and unattractive to rabbits. The prolific Campanula poscharskyana is left alone too.

Good luck!