It's called Sportscardword and the prices are absolutely insane! Nice guys though and quite knowledgable in their respective fields. It;s located in the heart fo the city in the prime shopping district so might as well check it out.
Link here:
Sports Card World: Home Page
If the weather is nice definitley hop a tram to Glenelg beach. Not sure what's on at Adelaide Oval (possibly domestic cricket) and there;s always something on or pending at the Adelaide Entertainment Centre or Festival Theatre if you or your missus is into that sort of thing.