It seems CorePlayer (among other apps) has new competition on S60 - JulyPlayer is now available, in (very) early version 1 form, for both S60 3rd Edition and 5th Edition and claims to play an impressive list of video formats. Trial versions let you test file compatibility and full versions are $10. It's early days though and both the interface and player performance looked like they could do with a lot of feedback from you guys (via their new forums) and subsequent iteration. See below for some screens. Comments welcome if you've tried it yet.

Formats supported are quoted as: "mp4,flv,f4v,mov,mkv,avi,asf,divx,wmv,m4e,m4v, 3gp,3gpp,vob,mpg,mpeg,264,h264,ts,ac3,ape, mp3,m4a,wma,flac,amr,aac,ogg,dat"