Never underestimate the utility of a large A-clamp with a mini ball head and cold shoe mounted on it; it can go many places that the Gorilla-style pods cannot. They are available off-the-shelf, but it can be cheaper to get the mini ball head and shoe, and just use hardware-store clamps and a short 1/4"-20 or 3/8"-16 bolt/screw to mount the head to the clamp.
And whether you like it or not, a light stand is often the quickest and dirtiest way of getting the job done, since one doesn't always have access to a handy attachment point for a clamp/gripper pod at the right height in the right spot. There are sturdy-enough-for-speedlights (but relatively short, generally under 8'/240cm) stands that are lightweight enough to bother carrying to location (~1kg) and will fold down very compactly (under 20"/50cm, often under 18"/45cm); having one or two of them along with lightweight umbrella swivels and collapsible shoot-through umbrellas (those will easily fit in most larger camera bags) isn't a terribly bad idea.
If you're okay with an extra shoulder-slingable bag (which could be a tripod bag doing double duty as a stand-and-modifier bag), then an Apollo-style softbox or Halo-style enclosed umbrella might be the next step up. They're not much heavier or slower to set up than a regular umbrella, but they're a bit on the long side when folded. (And there are some aiming/tilting issues with the Apollo that are easy to deal with in the studio, but require inelegant work-arounds in the field.) It's more to carry, but it also offers more control of the light. As with everything in this game, you have to find the right compromise for your working and photographic styles.
The trigger, too, is a compromise. Fire-only triggers are cheap and tend to be reliable, but they mean having to physically visit your flash(es) in order to make power adjustments. My favourite in this area is the Cactus V5 (low latency, long range and externally-available controls, along with the ability to set remote flashes to different channels to do the set-up then gang them for the actual shot), but it's hardly the only game in town. TTL triggers tend to be a little more finicky, but with the Canon system you can control your remote flashes even in manual mode from the camera. (Nikon is a little more limited in this regard; the camera-mounted unit needs to play the part of an SU-800 controller to get all of the features that the CLS offers.) The Yongnuo YN 622C seems to be the unit with the least negativity floating around, and while it's not free, it's not very expensiv as these things go either. A word of caution, though: older Canon flashes are electrically very "noisy"; they emit enough broad-spectrum RF that at very close ranges (as when the trigger is mounted directly to the flash foot) they can severely limit the range of a radio triggering system. A good (shielded) TTL cable to move the receiver away from the flash may help a lot if you are having problems with TTL functionality. (And you may need a "dumb" cable if you're using the flash manually with a fire-only trigger inside a softbox, since the reflective material doesn't reflect only visible light.)
Going forward, you may want to step up to Canon's own radio system as you can afford it. Your flashes won't last forever (nothing does), and replacing the 500-series units with 600-series units and perhaps the wireless controller will make things a lot easier in the long run - at a cost, of course - but there will be fewer widgets to keep track of, fewer batteries to manage, and fewer worries about ongoing compatibility (always a problem with third-party gear).
