A USB turntable is a simple and effective solution for the average home user who wishes to make a digital audio archive (MP3, AAC, etc.) of their vinyl records. You may not even have a turntable anymore, but want to transfer your collection -- you can then listen to it via a PMP/MP3 player, smartphone, tablet, or burn an audio CD.
USB Turntables also normally come with software for transferring and cleaning up analog sound -- clicks, pops, and hisses. They also typically come with the right audio cable adapters so you can use them on stereo systems that don't have a turntable -- this makes a USB turntable multi-purpose for either listening or transferring your vinyl records.
For less than $100, the AT-LP60-USB has a remarkably good feature set for converting your vinyl records to a digital audio format like MP3. It is compatible with PC/Mac and comes with the Audacity software to make it a great out-of-the-box solution. The belt-driven unit is directly connected to your computer or laptop using the supplied USB connector and vinyl records can be played at either 33 1⁄3 or 45 RPM. Audio-technica have also done a good job on the design of the turntable. It's solidly build and comes with features like: a professional aluminum platter; integrated per-amplifier (switchable), and a dual magnet phono cartridge that has a replaceable stylus.
There are a good set of audio cables included with the AT-LP60-USB too which makes it a flexible solution if you want to connect it to a system that doesn't have a turntable -- the included stereo adapter cables are: twin RCA (female) to 3.5 mm (1⁄8") mini-jack (male) / twin RCA (female) to 3.5 mm (1⁄8") mini-jack (female).
If you are looking for a budget USB turntable to digitize your collection of vinyl records straight to your computer, then the Numark TTUSB is worth a good look. It is compatible with PC/Mac and comes with the EZ Vinyl / Tape Converter software package which can be used to directly transfer to your iTunes library. Technical specs include: Anti-skate control, adjustable pitch control, 33 1⁄3 / 45 / 78 RPM (via software) speeds, and a built-in preamp for the line level RCA outputs. The Numark TTUSB turntable also comes with all the necessary cables for plugging into stereo systems or even transferring from audio cassette tape (1⁄8" mini-plug adapter).
Sony's PS-LX300USB turntable represents a well-rounded total solution for transferring your old vinyl records to a Windows PC system. You can either directly plug it into one of your computer's USB ports or use it on an existing Hi-Fi system via phono inputs. The turntable itself is belt-driven and fully automatic with the option of playing your records at the usual 33 1⁄3 or 45 RPM speed. As well as getting the turntable, Sony also includes their stellar audio editor, Sound Forge Audio Studio LE, which has some great digital audio restoration and conversion tools.