I'm really annoyed with dandelions. They had taken over both our front and back lawns well before we bought our house, and now I have to deal with the infestation. The photo at right shows a particularly bad example.
The weeding tool that came with the house helps immensely, but pulling these things out is still a giant hassle. We've got somewhat large lawns, and substantial portions of each lawn is covered in these little bastards. I was tempted to take a photo from the roof to illustrate, but that will have to wait until I've got another reason to be on the roof.
This is what the aftermath looks like once I get to them. The holes in the ground are disturbingly remininscent of dog and cat assholes. Gross.

My battle has been with clover. I have resulted to chemical warfare. The problem I have is that it merely stuns it, nothing has managed to kill it off.
Weed spray ftw.
I'm all ears if you have suggestions of sprays that a) are effective enough to actually kill these things, and b) don't leech a bunch of crap into the ground.
So far, no dice.
--D
Alternatives to weed spray:
1) eat them, as long as you haven't sprayed them yet.
2) weed flamer! Probably more effective than spray, but less toxic and more fun: http://www.groworganic.com/cgy_441.html
Eat them? I dunno. There are a lot of animals that like to poop in my yard.
I definitely like the flamethrower, though.
--D