mayfly
larvae 
mayfly adult
stonefly larvae
stonefly adult 
caddis fly larvae
caddis fly adultSize range - less than a millimeter for very young larvae, up to several inches for older larvae and adults
For more examples and a pictoral key to identifying aquatic macroinvertebrates, visit the New York Department of Environmental Conservation Stream Biomonitoring Unit's excellent site at: http://www.dec.state.ny.us/website/dow/stream/index.htm