There are lots! Maya Masala on Market St opposite Central Market, Harvest of India and Beyond India on O'Connell St, as well as at least one on Melbourne St and one or two down Rundle St that I don't know the names of.
There used to be one off of Hindley Street, in a side alley and downstairs. They had the most amazing Butter Chicken! I also love Beyond India in North Adelaide, who are definitely still there in O'Connell Street.