They make a reusable filter for you to use your own coffee. They sell them whereever they sell Keurig. It's not like a drip paper filter-it is a plastic cup with a little net filter inside where you place the coffee. Bascially a reusable K-cup. ;-)
I bought my Keurig in 2007, and I absolutely love it! Both of my sisters and my niece then got one, so now my whole family is on the Keurig bandwagon. For Christmas, we exchange K-cups as one of our small gifts lol!
I will never ever go back to a regular drip maker. I can always have fresh coffee when I want it. I can have a cup of flavored coffee without having to make an entire pot. I can decide I want a cup of coffee and not have to wait for an entire pot to brew-only takes the machine a minute or so to warm up from off and be ready to make a cup. If I have a guest over who wants decaf, I don't have to wonder about how to make 2 different pots of coffee at a time. We each get our own cup.
Keurig also came out with a "baby" version. It uses the regular K-Cups/reusable filter, but has a smaller water reservoir (ie would need to be refilled more frequently) and makes a smaller cup size of coffee. (On the larger models you can choose what size in ounces you want.) I believe it is under $100.
Actually the price isn't that bad. Some of the higher end drip makers run just as much. Breville (I believe an Australian company under license from Keurig) also makes a machine that uses K-cups that is either chrome or stainless. But it runs about $300. The regular Keurig has come down in price-I was in Bed Bath Beyond last weekend and saw they were around $120 something. Then you can use one of their 20% off coupons. Costco is selling Keurig for $119 and comes with 90 K-Cups.