I use the ElGato Hybrid
I use the ElGato Hybrid. It comes with EyeTV software and a subscription to TitanTV. I'm sure at some point they'll charge me but I haven't received a bill so...(I think it is 1 year?)
The tuner itself is about the size of an old-school thumb drive. You'll need an antenna (or if your cable supports Clear QAM) for a signal.
Do NOT plug it directly into the USB, use a USB extender dongle (redundant?). The elGato takes a coaxial cable and unless you are supporting the cable weight, it bends the connection.
Btw, you can hit up a radio shack for a simple DIY antenna if you want to go mobile.