This may sound an unlikely combination but bear with me.
We went round for dinner with friends on Saturday night and they generously dug out a half bottle of Chateau Suduiraut 1996 to drink with a rhubarb sponge and cream. That might sound quite a challenging pairing for an old Sauternes - and in truth the combination would probably have been better still if the wine had been a shade younger - but the pudding was quite light and, more importantly, the acidity of the rhubarb kept the sweetness of the topping in check making sure it didn't steal the wine's thunder.
The cream also helped as it does with sweet wines and sharp fruit - I can imagine rhubarb and panna cotta also working well.
As that lovely pale pink rhubarb is in peak season now I recommend the combination to you*. Other sweet Bordeaux or New World late harvest Sauvignon like Concha y Toro's Late Harvest Sauvignon would be a less expensive option.
The only thing that might throw it is if you cook the rhubarb with a fair amount of orange. In which case a late harvest Muscat might fare better.