Welcome to MFK, as you can see you'll get many responses regarding proper housing for your fish. As for your question, large oscars are heavy eaters and huge waste producers. You will need a large bio filter and equally large mechanical filtration.
You will also likely have to deal with high nitrate levels. Frequent water changes and gravel vacuuming will reeduce your nitrates. Also cleaning your mechanical filtration on a weekly basis will help reduce levels. So in choosing a mechanical filter you'll want to go with a filter that you can quickly and easily maintain. I use the Aquaclear 110 with I clean the large sponge on a weekly basis.
For biological filtration there is a wide variety of choices. A wet/dry sump is a great biofilter which will also increase your water volume, it turn this will slightly lower your nitrate levels. There are many different quality canister filters, eheims being regarded as the best. Personally I like the rena XP3s, which I set up with eheim filter media.
Using multiple filters is always a good idea. The AC110 will provide good mechanical and some bio, so if your main bio filter where to go down the AC110 will also act as a backup biofilter.
Good luck in finding adiquate filtration for your oscar, and feel free to ask as many questions as you need to.
