To increase usable density in your shelving these work well we alternate canned veggies and soup (sometimes we have to put one back in the top)
http://foodstoragemadeeasy.net/2009/02/16/build-your-own-can-rotating-rack/ the original plans here
http://foodstoragemadeeasy.net/fsme/docs/shelfplan.pdf can be modified to be taller to fit your storage height. After making a few of these I would add 1/8" in width and height to allow easier can movement. If you need help modifying the plans let me know, I have a copy someplace where I redrew it with the new dimensions.
There are some storage ideas here, perhaps some will fit in your existing cabinets
http://www.pinterest.com/diyboards/diy-kitchen-storage/
If you decide to remove your toe kick be sure to build up the floor slightly to prevent moisture at the floor level for cleaning or only use plastic/glass containers. Also, cut it out carefully as in most cases it does provide a significant support to the structure above, perhaps start with every other cabinet?
I've often seen bags of onions, garlic and herbs hung from the ceiling on hooks, that can be retrieved with a hooked stick.
If you decide to store under your sink be sure to use water safe containers, you might want to seal around the cabinet and floor area as well to prevent any leak to move at floor level. I could even see a drain line out with a vermin screen.
Some of these might work for your shelf spaces:
http://www.walmart.com/ip/10583489?wmlspartner=wlpa&selectedSellerId=0&adid=22222222227000017061&wl0=&wl1=g&wl2=c&wl3=40343530592&wl4=&wl5=pla&wl6=78306270632&veh=sem
A rack like this works well on a ceiling or a high shelf as the output location is lower
http://www.zesco.com/Amco-SM-10-Module-Number10-Can-Rack-Storage-System-pz015A195.htm be aware this is a #10 can rack and I haven't found smaller versions.
Magnet strips or pads can be screwed into the underside of cabinets or shelves to accept ferrous metal lids or vice versa; you can mount magnets to jars and provide a surface for them to attach to. This is ideal for spices with their light weight and shorter time availability.
Ok, let's leave the kitchen for a minute...
Under the couch, bed, in the bottom of the closet (add a shelf for the things you use frequently).
Find space that isn't used or cared for and find a way to fill it with what is appropriate for you. I have corners/edges in every space, that I don't use appropriately, they are locations of opportunity, we just need to find the appropriate method and somebody has done that, we just need to find it.