lots 不单独用的,lots of＝a lot of 后面接可数名词和不可数名词均可,接可数名词时谓语用复数,接不可数名词时,谓语用单数.
a lot 当然不是名词性短语了,而是副词性短语,修饰动词.比如：Thanks a lot.= Thanks very much.
再比如：I know him a lot.
plenty of 和以上lots of 和a lot of相似,后面接可数名词和不可数名词均可,接可数名词时谓语用复数,接不可数名词时,谓语用单数.