DC++ is a great program but the problem behind it is that you need to manually find HUBs to connect to and then leach. Not to mention several HUBs have a huge sharing limit. I recommend it, but not as your primary program. What I strongly suggest is that you get
Shareaza. Shareaza is an open source project that links various other p2p networks together. All of the other networks listed above by others, Shareaza lets you download from them. So rather than having more than one program, you can get the one program that allows you to download from all. Not to mention it has support for bittorrent.