is there a decent 55" set with passive?
The LG 55LW980 may be worth a look, still not seen one myself yet. Depends what you want the set to be decent at really. Passive 3D is considered better by some, though I think both have strong pros and cons.
LCD vs plasma for everything else, plasma wins for me in every way. Better motion for sport, lower lag for gaming, deeper more detailed blacks for films, more natural image for SD, no viewing angle restrictions, no clouding, back light bleed and no uniformity issues. LCDs can go brighter, cost a tad less to run, dont get IR and LED sets can be thinner.