Maybe 5 letters would be better since it leads to less confusion and is still much shorter than the normal, fully-spelled, name.
And in that case:
BRKWY - 2010 Breakaway
LUNCY - 2009 Lunacy
OVRDR - 2008 FIRST Overdrive
RCKRL - 2007 Rack 'n' Roll
AIMHI - 2006 Aim High
TRPPL - 2005 Triple Play
FRNZY - 2004 FIRST Frenzy: Raising the Bar
STKAT - 2003 Stack Attack
ZNZL - 2002 Zone Zeal (Didn't see a better way
)
DBDYN - 2001 Diabolical Dynamics
COOP - 2000 Co-Opertition FIRST (Also didn't see a good way)
DBLTB - 1999 Double Trouble
LDRLG - 1998 Ladder Logic
TRDTR - 1997 Toroid Terror
HXNHV - 1996 Hexagon Havoc
RMPRL - 1995 Ramp n' Roll
TWRPR -1994 Tower Power
RGRG - 1993 Rug Rage (Also didn't see a good way)
MZCZ - 1992 Maize Craze (Also didn't see a good way)
Granted, some 4 letter acronyms are perfect and they can't really be improved just by adding an extra letter.