The standard AeroVee air cleaner uses a replaceable paper filter element. Although the element appears adequate, I found that the engine turned up about 100 rpm faster with no air cleaner than with the paper filter. This suggested that the standard filter element was too restrictive for the engine.
The filter dimensions are 2" high x 4" diameter, and K&N makes a filter (E-3120) that matches these dimensions. K&N filters have a reputation and efficient, durable, and high-flowing, so I purchased one and I now run that in place of the paper filter. Additionally, the K&N can be washed and re-used just about indefinitely.
For more information, see http://www.knfilters.com/search/product.aspx?Prod=E-3120
I purchased the filter from Jegs for about $28, but you may be able to order it from a local auto parts store and save the cost of shipping.