If you travel much with a carry-on case, then you'll appreciate an equipment bag that has 4 wheels as opposed to just two. I myself use the "Think Tank Airport Roller" (found here) quite often. LowePro has recently offered up a new Photostream SP 200 Roller Bag. The Photostream is a less expensive option if you're looking for a dedicated equipment case on 4 wheels that also works with carry-on size restrictions.
Lowepro SP 200 Roller Overview
The PhotoStream SP 200 has exterior measurements of 13.8 x 8.8 x 21.7" and weighs 9.7 lb when empty, matching carry-on requirements for most American airlines. For keeping small items such as cables or lens caps, two zippered mesh pockets are conveniently located on the lid interior and allow for easy access to your accessories. As for transport, the case comes with a three-stage telescoping handle and four 360° wheels for easy rolling. When hand carrying is needed, you can use the integrated handles found at the top, side, or bottom of the bag.
Nylon and EVA hardshell case optimized for air travel
Holds 1 or 2 professional DSLRs or mirrorless cameras, plus 4-8 extra lenses, flashes, battery grips, etc.
Set of customizable padded dividers can be adjusted or removed to find the best setup for your gear
Hinged front panel allows easy access to your laptop or tablet without opening the entire bag
Dual zippered mesh pockets for keeping small accessories such as cables, batteries, and memory cards
Lightweight telescoping handle made of aluminum, center button allows you to set it to 3 different stages
4 wheels with 360° rotation for easy and intuitive transport
Integrated handles on the top, side, and bottom of the case for carrying by hand
Exterior dimensions of 13.8 x 8.8 x 21.7" meet carry-on requirements for most airlines
Here's a great little roller bag kit that normally runs well over $200 dollars. The kit can be separated into two separate bags or just used as one padded roller. The small roller can be emptied to hold clothes, and a padded insert can hold a camera body + lens with two additional lenses and room to spare for a laptop computer. On Amazon they are still listing the X50 for $213 (seen here). Currently on B&H they have a huge huge discount dropping the price down to just under $80 bucks via B&H (click here).