As I-Blocklist have now started charging, does anyone know of any alternative free lists, particularly P2P lists?

I use
http://john.bitsurge.net/public/biglist.p2p.gz
Found it on https://giuliomac.wordpress.com/2014/02/19/best-blocklist-for-transmission/

You're actually not correct in saying that. They are only charging for certain blocklists, not for all blocklists. If, say, you were used to using Peerblock and only using the blocklists that PeerBlock used by default then they (and several others) are still available for free from I-Blocklist. Just check the webpage and you will see this is so: https://www.iblocklist.com/lists

Radish, check your link. They just started charging for everything!!! All of it is now subscription based when it used to be free.

I just looked at myself. You seem quite mistaken, there are many free lists. Just add Level 1-3 to your block lists.

I've been having problems with this lately, every few days it drops to about half the IPs blocked and slowly builds up to 2.5 billion blocked (what it should have) and then drops down again. Something must have changed that interferes with his algorithm.

Usually I get thousands of blocks with this list every session but when it drops down I only get hundreds.  There is more info and different blocklist discussion here https://gist.github.com/johntyree/3331662  but this code really needs to be fixed.  I recommend once you see it blocking around 2.4-2.5 billion addresses you stop it from updating for now.

https://iplists.firehol.org/

This is completely useless, see my reply there: https://forum.tixati.com/support/1992