So be good to your fish, living in filthy water would be like living in a smog covered city like Beijing.
So enough preaching, your choices are
a. underground filter (are you living in the stone age),
b. power filters and biowheels (affordable, though the filter changes can add up),
c. canister filters (can be $100 at the low range $200 at the higher range + is you can wait 3-6 months to rinse out the media or change it),
d. fluidized filters (growing in popularity, uses sand and a filter pipe where the water is pumped through).
Ps here is great guide with illustration on the different filtration options you have.
Be careful in your brand choices, go with the industry leaders which each have their own advantages from price, to type of media and reliability. A knock off brand from China is disaster waiting to happen and how will you get parts??? Here are your brands for all types of filters.
Eheim, Marineland, Hagen, Fluval.
I chose to go with a canister filter because I wanted excellent filtration and low maintenance. I had tried the biowheels and found them to unsightly hanging off the side and noisy. I also notice a white film begins to builds up and it is easy to be obsessive about changing the filter pad when it so easy to check. It seems half the battle is leaving the filtration alone for a while.
The advantage of Canister filters is they usually only need to be cleaned once every three months. You really should not replaced the pads, especially the ceramic pieces unless they are literally disintegrating from my readings online. The media including the pads needs a rinse off. The one caution is carbon (black) filters, they need to come out after a few weeks because a carbon filter will actually hold the waste and does not allow biological breakdown like the ceramic media, it will actually begin to release toxins.
I think power filters/bio wheels are a good way to go if your tank is under 30 gallons or less.
Next post will be out the filter I chose and more importantly how to install it because the directions are not helpful to say the least despite it being the top rate filter for price and quality after reading many, many review.