The most frustrating thing about bad drivers, is that 99% of them just drive off, leaving you ranting and raving at the side of the road. You never get the last word....
So..."The London Solution":
ONE OF THESE...

FILLED WITH THIS...

I wouldn't necessarily recommend the above, but for some people I'm sure it presents a satisfactory solution.
On a serious note, most PSVs are fitted with CCTV now, inside and outside. If you get chopped up by a bus, and you get it's registration number - make a complaint to the bus company. If they just fob you off, serve them with a freedom of information request and demand a copy of the CCTV footage:
http://www.direct.gov.uk/en/governmentcitizensandrights/yourrightsandresponsibilities/dg_4003239
The bus company have a legal requirement to resond to your FOI request within 20 days. This is a real pain in the backside for the bus company, so most of the time they will cave in and issue you with an official apology, and / or at least deal with your complaint seriously.
Likewise, if your incident was within sight of ANY street CCTV, you can make a FOI request to the Police for a copy of the footage. In complying with your FOI request, they will inevitably view the footage. If the footage does show any criminally bad driving, they will have a duty to follow it up for you.
As for car drivers who leave me fuming - I try and catch up with them at the next set of lights (Which I usually do). They are usually absolutely horrified when, trapped at a red light, you pull up to their drivers window and ask for a polite chat. I smother them with kindness, call them Sir, or Lady, and generally give them a hard time about their bad driving, with impeccable grace. I like to think they may remember the experience, rather than simply dismissing me as just another angry cyclist.
P.S. I've got one of these on my commuter:

Its great in traffic, really suprisingly loud, and unlike air-horns, it sounds like it belongs on a motor vehicle. This suprises many drivers who have simply not looked / not seen you, and a sure-fire way of letting bad drivers know your feelings. I find it most useful as a preventative measure, if I see someone about to cut me up, I give them a blast, and quite often they have second thoughts about what they are about to do.