If you just want to stick a cheap flash on your camera and have it work well- the YN 468-II is the flash for you.  Currently selling for less than $90. Canon Compatible 468 II | Nikon Compatible 468 II Note - your camera model may not be listed on the page but it will work with your camera if you buy the right brand and you have a DSLR made by that company in the last 10 years. 

YongNuo YN-468 II Speedlite With LCD Display E-TTL(Canon) or i-TTL(nikon)

This is the cheapest Yongnuo flash that does E-TTL/iTTL - this means the camera and the flash can talk to each other and the flash will adjust the output of light to create a proper exposure.  This is the easiest and most painless way to greatly improve your indoor photography.   Additional features include Manual mode with power adjustment from full 1/1 to 1/128 in 1/3 step increments.  Multi strobe mode  fires a series of flashes in one exposure (Example coming), Slave modes in S1 and S2. As far as I can tell the only difference between S1 and S2 - in S2 mode the Yongnuo will not be triggered by the test flash. Slave mode allows you to fire the flash when it is not attached to the camera.  You will need a camera that has wireless flash capabilities.  As I said in the opening this is the best value for generally better flash photos. Rotate the head over one should and point it up about 45 degrees - the room will be filled with pleasing light and your photos will look better.   You can manually zoom this flash from 24-85 or if you believe the camera settings 24-105.  And the flash does allow high-speed sync(I will explain this soon - it is useful for shooting outside in bright light or shooting higher speed action).Buy from Amazon Canon Compatible 468 II | Nikon Compatible 468 II

Yongnuo YN-565 EX TTL Flash Speedlite

What does $20 more get you over the 468 II?  Slightly faster recycle time and the ability to power the flash from an external battery pack and wireless TTL - So the 565-EX is able to communicate with the camera when it is off or on the camera.  It does lack high speed sync.  I see more folks reporting problems with this flash versus the 468 II. It may be that they expect more or use the flash harder?  Still the reviews are generally positive.  The back of the 565 has more buttons and larger LCD screen.  The comparable Canon flash is the Canon 580EX which costs roughly $400.   Pretty significant difference.   Would I walk into a professional shoot using this as my only flash- it is unlikely. I think these flashes are great for personal use, family functions and I would certainly bring along one or two as backup but there are just enough reviews that say they can be quirky that it makes me hesitate to recommend for professional use.  In working with the 468-II idid have it freeze up on me once. In fairness I have used the 600RTs and had issues - no flash or product is 100% fail safe but the level of quirkiness is just high enough that it makes me hesitate.Buy from Amazon Canon Compatible 565 EX | Nikon Compatible 565 EX

Yongnuo YN-568EX II

These flashes cost $180 - The extra $100 over the price of the 468s gets you a flash that is powerful and capable of controlling other flashes along with very high speed sync  - up to 1/8000 of a second.   Reviews are less positive but still generally good, leading me to believe my theory of higher end flashes used by professionals that expect more.  And it comes with a diffuser cap and the head does rotate 180 degrees (this is actually quite beneficial and I mention this in my long video review)Buy from Amazon Canon Compatible 568EX II | Nikon Compatible 568 EX

Yongnuo RF-603C
	These are not flashes! These are wireless triggers that are capable of firing an off camera flash without using the on-board flash of the camera.  Watch my video discussing and showing how to use the RF-603C triggers.  Range is reported to be reliable up to 100 meters. These are manual only- you do not get ETTL or any wireless control of the off camera flash.  They are also capable of remotely triggering your camera. That is what the small cord is for in the photo. Be careful to buy the right set if you want to use it as a remote. For actually flash firing you only need brand to match. Price ~$30.  Watch my video discussing RF-603C and then Buy from Amazon Canon Rebel Series(t4i, t5i) including 60D/70D | Canon XD series and older 50D/40D etc | Nikon D3XXX, D5XXX, D7XXX series
Yongnuo YN-622C
	These offer wireless control - Smart control of external flashes. Throw one on your camera and plug the flash into the receiver and you have the ability to control the flash as if it were sitting on top of your camera. I have these in hand and will be doing a complete review soon. Buy Yongnuo YN-622 from Amazon

 B&H Now carries Yongnuo Products and has a nice page listing ALL Yongnuo flashes, lenses and flash triggers. See Yongnuo on B&H Photo Video