Project make a decent range of turntables and are probably the best respected in the <£150 market. I think they also do a USB version but that might add a few more quids. As spt points out, you don't
need a USB turntable to convert vinyl to MP3 (or whatever), you can just plug your turntable (or an output from your amp) into your computer and use audacity to do the conversion - you can download audacity for free.
It is a bit of a faff though (for me, for example, I have to unplug the turntable and lug it upstairs if I want to put a "proper" record onto the mp3 player.... And if you use the turntable without a pre-amp then you need to amplify the signal using audacity which adds time to the process. And there are various options for tweaking and tidying up the sound).
If I were you I'd consider whether you'd primarily be using your record player to play records (
) or whether you'd want it mainly to digitise your collection. In other words how much the convenience of a USB turntable would be worth for your own circumstance. If you aren't going to use it much then you'd probably get better sound quality for simply playing records from a decent budget hifi turntable.
God that was a boring reply. Sorry everyone!