General Motors raised its cash rebate sales incentives by between $500 and $1,000 on most of its 2005 model-year vehicles on Wednesday, according to a Reuters report. GM also extended an offer of additional bonus cash of between $500 and $1,500 for consumers who finance a loan or lease through GM's finance arm, General Motors Acceptance Corp. The new incentives come a week after posting an 8 percent drop in August sales.