Overlooking Different Muscles
One thing that is overlooked in 95% of these cases is the shins. Calves are the relatively large, meaty part of the lower legs that is obvious as the area to train. However, you DO have muscles in the front as well! These are not as large and not nearly as powerful as the calves, but they are THERE. And more importantly, they contribute greatly to the overall impression of your legs. Think about it: the Hamstrings aren't really something you notice - unless they're not there!
By training your shins regularly, you're adding a whole new dimension to your lower-leg training. If you add just a little bit of mass on the shins, you increase the overall circumference of the lower legs even if you don't increase the calfs at all, creating the illusion of progress. The best solution is - of course - to make gains on BOTH areas, which will make your lower legs seem like they're about to blow! And the good news is that shins are usually easier to get to grow, since they are under stimulated to begin with!
Hammer Strength Machines
One of the easiest ways to hit the shins is to use a special shin-machine. Hammer Strength makes one of the best I've used, but there are others that are good as well. If you haven't used one before, it's a pretty small little thing where you wedge your foot in between two pads and start raising the toes as high up as you can. Needless to say, you'll not be using 45's on this one. I find it best to sit on a bench and hold my knee fixated while squeezing the bejeezus out of each shin before moving to the next one, but if you prefer standing, or sitting while doing both at the time, then by all means, do that.
Various Hammer Strength Machines!
However, I realize that a lot of you work out in home gyms, or have to make do with lesser equipped commercial gyms, so there's an alternate way that also works well: Pile a stack of plates next to something you can hold on to. Then stand on one foot with the heel on the edge and the rest of the foot out in the air.
Keep Good Form
Lower the toes until they're pointing as far down as they can, getting a good stretch of the shin and ankle. Do the rep raising your toes up as high as you possibly can, consciously contracting your shin, hold for a second, and lower down to the stretched position again.
As you get stronger, you can hold a dumbbell in your free hand (the other hand should be used for balance, but make sure not to lean on the support too much). Also, you might want to make sure the plates are steady. If not, use something else with a distinct edge that will elevate you enough.