So I got a T3i brand new this summer and this winter I want to get a nice lens. Since I do mostly right now action shots I wanted to buy a 100-400 EF L lens. Is it worth the $?? Or tell me about any other lenses that you like that are a zoom lens and at least 400-500 at top magnification. Keep the cost low!!

The 100-400 is a very capable lens in good light but I wouldn't want to use it
at an indoor sports venue. For that I would recommend a 70-200 2.8 or a
fixed focal lens for that (i.e. 85 1.8, 50 1.4).

If you tell us what kind of action photos you take (indoor, outdoor, day, night?) we can give you a better
answer.

Usually outdoor. Baseball, hunting, just things outside. I need a longer range lens

Originally Posted by ipatry Usually outdoor. Baseball, hunting, just things outside. I need a longer range lens

100-400 would probably be fine, provided you aren't doing anything in low light/night time. The lens does have IS, which is helpful, but once the light gets low, it becomes difficult to get any action with floating aperture lenses like that.

Unfortunately, this is equipment which is manufactured with high quality materials and precision and keeping the cost low is difficult. If you want low cost, look at Sigma/Tamron/Tokina etc. They're not on the level of a Canon product, but they will probably satisfy most user's needs.

Originally Posted by ipatry Usually outdoor. Baseball, hunting, just things outside. I need a longer range lens

the 100-400 is a nice telephoto zoom but first try the Canon 55-250IS - it's sharp but inexpensive ($150)