Hey, kitbashers (  is it me or is there something slightly obscene-sounding about that name?  )  !  Share with us some of your sources for good greeblies and kitbashing salvage!  [Anyone who doesn't know what greeblies are, so are the little bits that break up a kitbashed model's regular form and make it look custom.]
Here are a few of my favorites:
Old computers:  tear the motherboard out and there are all sorts of things that you can pluck off and put in your bits box.  Needle-nose pliers can be a lifesaver here.  I recently added a rocket launcher to the back of one of EM-4's fighting robots by using some kind of plug that goes into the back of a CD-ROM and three cut-down straight pins.
Coffee stirrers:  the little plastic straw kind can be useful for conduits, gun barrels, road barricades, etc.  The plastic ones that look like two little straws glued together side-by-side make nice electrical conduits for your sci-fi settings.
Hair curlers/rollers:  a neat source of engine cowlings, roll cages, etc.  Cheap and easy to use.
Sprue:  obviously a good source of plastic for whatever you might need.  I use it for landing legs, weapon mounts, etc.
Window screen mesh:  available in both metal and vinyl, it's great for fences, Mad Max-style vehicle window coverings, sci-fi walkway flooring, air duct covering, and so forth.  Some people also use auto-body repair mesh.
Household bottle lids and caps:  a cap from an Aleve bottle (  a painkiller available in the US  )   makes a great sci-fi-ish turret.  Other caps make good hatches, ring mounts, access covers, armored wheel hubs, and so forth.
Bamboo chopsticks:  great scratchbuilding material, being both strong and easily drilled.  I've seen an entire Vietnam watchtower built out of chopsticks.
"Egg crate" lighting panels:  these are panels that go in office-style overhead light fixtures, and have 1/2" square holes in them (  here's an example of some being used for a different project: balinka.com/pdfsetup.htm  )  .  Good base for sci-fi walkways (  covered with window screen mesh  )  , gantry cranes, and perhaps buildings.
Anything in the electrical aisle:  Your local DIY store or Home Depot is a mecca for kitbashing.  The electrical aisle alone has loads of good stuff:  outlet sinks can be used as small utility sheds (  think I saw that on Terragenesis  )  , while I've used some little square bits as feet for my dropship's landing legs.
Disposable razors:  don't throw away that Bic!  The handle makes a dandy boom crane, while you can glue together multiple caps to make a ventilation louver or whatever.
Plastic cutlery:  Disposable plastic forks, knives, and spoons can be a good source for making spiky bits (  you Chaos 40Kers know you can't resist having more spikes  )  , reinforcing structure, or adding mysterious domes to your alien attack craft (  "oh, yeah, that there's the magneto-anti-flux-proto-grav-tesla-flibbert drive sponson.  Glad you asked?"  )  .
I know there are many more sources, some of which I'll think of and post later.  Where do you get your greeblies?