Very few as far as I know, most plants dont take to kindly to salt in the tank. The following is a list I got from the tropica website, all apparently are ok in brackish water not that I've tried it though.
Aponogeton crispus
Bacopa monnieri
Cladophora aegagrophila
Crinum calamistratum
Crinum natans
Crinum thaianum
Cryptocoryne wendtii 'Mi Oya'
Glossostigma elatinoides
Lilaeopsis brasiliensis
Lilaeopsis macloviana
Microsorum pteropus 'Narrow'
Microsorum pteropus 'Philippine'
Nymphaea lotus (zenkeri)
Samolus valerandi
Shinnersia rivularis
Taxiphyllum barbieri (Vesicularia)
Sam