hmm i've only heard the stuff she did with Tricky, and with Massive Attack on their latest EP.
Tricky is great, but i think most people won't appreciate him on first listen. take a look at Maxinquaye which is one of his more accessible albums that includes Martina, and see what you think.
i see that she has 2 solo albums - i know what i'm downloading today
edit
listening to Quixotic right now. reminds me of Zero 7 with more soul. good stuff!