Good & cheap speed lights (pro please)?

I'm looking for a decent flash for my Nikon d5100. I also want a couple of transmitters and receivers and a stand for the flash.

This one was really helpful

If you buy a Nikon SB-700 or SB-910, you won't need a transmitter and receiver, so that makes the price more palatable. You D5100 can trigger these flashes in Commander mode. (See "creative lighting system" or "CLS" in your manual.) There may be times when the optical trigger does not work, but personally I have not encountered that yet.

I use cheap Sunpak tripods for my off-camera speedlights.

As I mentioned before, I use the Yongnuo YN560 (it costs around £50).It's a good, powerful, all manual flash. About the same output & spec as a Nikon SB800 - zoom/swivel/bounce head. Fully manually adjustable in power output from 1/1 (full power) down to 1/128 power. As well as being controlled by triggers, it has an optical slave mode too, so can be triggered by another flash.

In respect of your other Q about triggers (after the question closed), the trigger as a whole comes in 2 parts - the transmitter that sits on the hotshoe and the receiver that goes onto the flash 'foot'. Both of those parts are together what makes the 'trigger'.

The RF602 triggers (also made by Yongnuo) cost about £20 a set (that's one receiver + one transmitter). You can buy extra receivers for extra flashes.

As for stands, I bought a couple off eBay for £24 - can't access the link right now but I'll add it later. These are lightweight stands, fine for speedlights. The YN560 speedlight will come with a diffuser and a little flash stand (like a foot) as well.

Since you want trigger you will need to adjust the flash power manually, you can try to find second hand Nikon sb24 & sb25, I got mine for $100.

If you want something newer you can find second hand sb600 or sb800 (this one is better than the sb600 & sb700, you can use it as a master flash in order to control slave flash like the sb600 & sb700 or master flash like the sb900 & sb910)

If you're looking for something new you have the Nikon sb700 or the sb900 & sb910 (those two are similar to the sb800, there's not a huge difference in term of power, for the price I would pick up two sb800 instead of one sb900 or one sb910).

As for the radio trigger, if you think in the futur will make some money out of your photography I strongly suggest you stick to pro trigger for the only reason that they always work (pocket wizard, cybersync, elinchrom), unlike the cheap trigger that occasionally miss fire.

If you're looking for something good for an enthusiast amateur you can look up the Cactus trigger V5 (those are cheap trigger good enough to have some fun).

The light stand, if you can get at least a 7 feet tall.

You could buy yourself a cheap white translucide umbrella and a bracket like this one to fix your flash and the umbrella.
http://www.bhphotovideo.com/...table.html

If you use it outside make sure to put some weight on the light stand, otherwise the wind can swing your equipment on the ground.