Many issues here. Let me go over in as much detail as possible:
Background: I love energy efficiency, and when doing my kitchen researched this LED Vs CFL vs incandescent lights extensively. Notice there are also permit (legal) implications, depending on which state you leave (CA has Title 24 for example).
Connector types: There are several connectors that make the decision of which light you can use tricky. the main ones are
Edison: The screw type, accepts CFL, Incandescent and some LED bulbs
Pins (2 or 4): Accepts florescent. Was invented mostly so that for permits purposes, they can make sure you are installing an efficient light and will not go and replace the CFL bulb with an incandescent one after you pass the permit.
GU10: mostly used for high voltage halogen
GU5.3 Bi- Pin: mostly used for low voltage halogen
High level rules:
You never go with incandescent when it is incandescent Vs CFL (Edison, screw system). LEDs are getting there, but not enough to justify the price and their light output is very low.
You can only go with pin florescent if you have a florescent "hw". that is the only thing that you can plug there by design.
Never use Halogen. If it is a GU10 (line voltage), get a $20-$30 LED (MR16). you get 4W Vs 35W. Light output is lower, but you can get HW with simply more heads. Replace 3 halogen with 5 LEDs and you are fine in terms of light and energy savings
If the halogen is a low voltage, things get tricky. You can just replace the head with a 3-5W bi-pin LED. they run $10-$20. They problem is that you need to make sure your low voltage converter will work. converters have what's called "minimal load". For most of them, they expect a 35-50W halogen so they have a minimal load of 10-20. That means that when you plug a 3W LED, they may not kick in. you solve it by either using a remote transformer that feeds "enough" LED bulbs, or get a transformer that is "led" designed, but really all it means is that it has a minimal load of 3w and goes all the way up to something (I have a 3-60W for mono-points).
Lat general tip: do not mess with dimmers. Just on/off.
My personal choices:
For kitchen recessed light I got LED LR6-GU24. It is 12W, think that the florescent way would suggest I put a 23W bulb for each of these (I have 7). That means 50% saving. Same light output (they say it is 65W equivalent, but it feels like closer to 90W). No one can tell it is LED BTW, it is bright and even (not a "pin" of light, and well spread).
Cost efficient: great! less energy, and upfront cost was the same as getting a florescent can combination. (you may get cheaper florescent if it is not for a permit and you do the Edison type)
For a bat lights I went with 3 mono points. Each has a transformer built in. I did not (suggest you never) buy "LED" lamps since you pay a huge premium for getting the LED HW. I just got the transformer with minimal load of 3W. I then threw away the GU5.3 Bi- Pin halogen and got Maxxima LED MR16. They are very good price (value) company. I compared the light to a $30 GE and these one are just as good. Notice that at 3W it is indeed just ambient light. good for over the bar in addition to some other light in the room. If you need more power, get 4 or 5W bulbs. see maxxima site
For spotlight lights in the center of medium size room, I went with much cheaper "line voltage" fixture from Lowes. These fixtures expect GU10 halogen (25-50W). I got in this case a the more expensive $30 LED GU10 bulbs (GE, at home depot). They are great, but I hope you can do better on the price. I have 5 and for medium size dining room, correctly targeted, it is nice light to use while eating.
It makes sense - look for "low voltage LED Lighting" to see what's available, or slide on over to Electronics to build your own.
Dimmable LED bulbs are those with drivers built-in that are "dimmable" - if just running controlled current to LEDs, they are all "Dimmable" (lower current, lower light) so, no, you don't want an LED described as "Dimmable" (nor one described as 12V, probably - a "bare" LED with no other parts attached is best when you are going to feed it controlled current.) If you purchase a "12V dimmer" pre-made, follow the dimmer-maker's suggestions on types of LEDs to attach to it.
LEDs are current devices, so controlling the current will give highly consistent light output (controlling the voltage, less so)
Best Answer
Be clear on the things which plug into AC power and the things which don't. The things which do, must be UL-Listed, or an equivalent testing lab such as CSA or ETL. These marks are absolutely useless: RoHS, CE, CCC, FCC.
There are actually 3 separate things here.
A generic 12 volt power supply.
Any common 12 volt, constant-voltage (i.e. normal) power supply will do. You can use a hacked PC power supply. A car battery. The output of a solar charge controller. A 12V battery charger. Eight D-cells. Whatevs. Doesn't matter.
This is not a driver. A driver is a special thing designed to drive individual LED emitters or strings of -- yeah, I can see where that would be confusing. LED drivers are used with raw LED emitters (i.e. the raw parts from Cree) which need to be driven at a specific, exact current (but voltage could vary all over the map). Drivers are used for appliance LEDs like you might find in an IKEA floor lamp where there are 18 LEDs that need to be driven at exactly 350ma at some voltage between 52 and 80 volts. That is not what you have. I'll discuss later how LED strips regulate current.
You just need any bog-standard constant-voltage 12 volt supply that come in an endless number of forms. In LED strips, the power supply has no role whatsoever in dimming. (actual drivers do, but as said, you can't use a driver.)
The dimmer (or if color, the controller)
This module takes power in from the 12V power supply, and outputs PWM power for a limited number of LED strips.
An interesting fact about these is the same unit can usually work in a 24 volt circuit (24 volt PS + 24V strips).
Now, if you need to drive more than 2 amps worth of LEDs (or whatever the dimmer's rating is), you can use its output as a signal instead, and feed it to an amplifier. Most amplifiers are 3-4 channel for color LEDs, but you can just feed all 4 channels with the same signal.
The LED strips proper
Remember what I said about drivers? Your strip is cuttable every 2 inches or so. Look closely at a single segment: you will find 3 LEDs and a mystery part. The mystery part is a resistor, and its job is to be a current-limiter; it's a very simple, passive version of a driver.
If it's that easy, why do the other ones use active drivers? Because they're driving the LEDs very hard, as close to the manufacturer-spec redline as possible... which means, they must put large heat-sinks on the LEDs. These strips don't have heat-sinks, so they are driven at modest levels. This is less cost-efficient, but golly, you can hardly complain about the price.