Recommend me an external USB sound card please

I've been doing a bit of recording from and to cassette units, so I was leaning toward getting one of these:

http://cachepe.zzounds.com/media/quality,85/brand,zzounds/fit,400by400/ua1x-29bd37547aa8e8ed4726b1017c9ace57.jpg

Which has RCA ins and outs plus headphones for monitoring.

However, I've started doing a bit of mastering and general processing on my (pretty old) PC, and I don't think the soundcard that came with is really up to scratch.

My only requirements are the aforementioned RCA plugs (although adaptors wouldn't be too much of a stretch if there's nothing suitable that has them), and cost (Hopefully not too much).

Thanks.