BrandyVSOP Loc: Oregon USA

Looks to me like you need some reach, so I would say the 400mm L 5.6, or the 100-400mm L 4.5-5.6. I have both. The 400 I got on Ebay, the 100-400 I bought from a member of my photo group...

lizardworks Loc: Western Slope of Colorado

Vi, if you think you want to try one of these lenses, check with B&H or other big camera stores about renting one, so you can truly understand what they do. The other thing to remember-"L" lenses hold their value very well, so if you decide to sell one you'll get most of your money back out of it. Check e-bay for new and used "L" lenses.

the f/stops here Loc: New Mexico

Not knowing what images turn you on, I'd probably say trade in 3 of your four lenses, keeping the 18 -135, and buy a lens with better optics. The 100mm f/2.8 IS L Macro lens would be terrific if you like to do close-up photography. The 70-200 f/4 IS L lens is a lens that will give you great images that you 70-300 just can't provide. Consider the 100-400 IS L lens that has provided professionals the ability to capture great images from a distance. Those are just 3 ideas. I can't tell you which lens to pick but I can tell you "PUT YOUR MONEY INTO OPTICS AND NOT CAMERA BODIES!" I am a pro and I do not sell equipment.

imagemeister Loc: mid east Florida

I have already married my 70-200 F4 L ! - Cheapest L lens there is W/O IS. Sharpest lens I have EVER used - even with a Tamron 1.4X which stays on 95 % of the time. This set-up stays on a monopod 95% of the time and is compact and lite weight.

BrandyVSOP Loc: Oregon USA

I just got that lens a few months ago, I am loving it too!
I bought it from a camera buddy in one of my groups for $450.00.

I am posting this image in your thread just to show a recent image I got from it!

NoSocks Loc: quonochontaug, rhode island

i'm not a canon shooter so i can't help much except to say that you have no prime lenses in your bag. a fast 50 or 85 might make sense. i'm waiting for the 85 and drooling every day.

foghornleg90 Loc: All over USA - Medford, OR & Knoxville, TN

How far away and how close are the 'things that move' (that you shoot)??

Personally, 75% of my motion shooting is done with either the 35-350mm (L) 3.5 to 5.6.... or the 70-200 (L) IS 2.8. Either can be touched used for less than new... both are serviceable by Canon USA, as long as they aren't hot and aren't black market lens (Canon USA won't service black market lens). Either one is about $1800 for a good one.

Canon also has a 28-300 (L) 3.5 to 5.6 IS - that is sweet, but over $2200. And the 100-400 (L) 4.0 IS - that is great if you are never closer than about 30 feet of a 6 foot object. (The 100 to 400 is awesome for baseball, good for football if you aren't on the sidelines - but sucks for most all other people sports, unless you can't get on the sidelines).

The 35-350 & 70-200 are the preferred basketball lens...

Anyhow... investing in great glass is always worthwhile, IF you are going to use it, and can make money with it. Otherwise, learn to work what you have for now... and save up.

Another thing, you might find a 'renter' - like Borrow Lens... and rent some different lens for a few days... see how you like them BEFORE you buy. I hear that Tamron has an AWESOME EF 70-200 f2.8 for under $600 that competes pretty good with Canon's $2500 L IS II, and beats the non-IS version. But, I've not tried it myself.

Best of luck... and I've had good experience with rentals from borrowlens.com and a few other renters... worth looking into.