Winamp 2.xx for mp3s (i didnt like Winamp3)
Power DVD 4.0/XP for DVDs and MPEGs (for the TruSurround effect)
Windows Media Player 9.0 for WMV (no other player plays these files)
DivX for AVI (no 2 questions about that)
Real One V2 Gold for Real audio/video (this version is cool)
VCD Cutter to cut the MPEG clips (i dont know of any other software

)
Smart Ripper to rip DVDs (happy with this one)
wow i didnt realise i was using so many players so often. but mostly its Winamp and Power DVD that i have short-cut keys for on my keyboard.