How do I clean chain grease off my clothes?
Most ordinary baby wipes will get grease out of clothing if you get to the stain quickly enough - or, at least, get enough of it out that the rest will later wash out. You can also carry spray-n-wash pads or keep them in your desk at work. However, baby wipes are also good for cleaning your hands - handy after changing a flat, or fiddling with a bike chain. 

However, it's even better to avoid getting grease on your clothes to begin with, so I suggest using a pants clip or rolling your right pants leg up. A full chainguard is great for this, but it's not always practical on a commuter bike. This won't prevent the problem completely, bit it does help minimize it. 

For these reasons, I found that when I was commuting, I tended to favor my black or dark-colored pants.