www.shareaza.com
It is open source. The code is on source forge and freely available to anybody, this makes it impossible to put spyware/adware/malware in it.
Download it from that site and that site only. Other places on the internet have distributed fake/modified versions or try to get you to pay for it.
If you're computer is fucked up from spyware:
http://www.lavasoftusa.com/
Some antivirus software such as Trend Micro will scan for some adware/spyware as well, free online scan available here: http://housecall.trendmicro.com/