Not a toolbar, but if you search through Bing, you can get credits which can be converted to AA miles. The current exchange rate is 413 credits => 100 miles. They cap the number of times you can get credited for searches per day (excluding small number of additional easily achievable credits). I can get 100 miles in just under a month. Not the best way to get tons of miles
This is also the only way to get miles with web search I know that works with Macs.