Garrett makes several "families" of turbochargers that are targeted for different sized engines, HP goals, and drivability characteristics. Crafty tuners, manufacturers, etc, have mixed and matched these components to produce hybrid turbos that can provide the benefits of several turbo families. The possibilities really are endless, but I'm just gonna list some common ones or else this post would be reeeeeeallly long.

Turbocharger families
The T25 family = super fast spooling "small" turbo that makes good low rpm torque, but lacks top end power. This turbocharger is commonly used where throttle response and low rpm torque are desired without much regard to high rpm power.

The T3 family = "intermediate turbo" that spools slower, but has the ability to make substantially more power than the T25 family. This turbocharger has been used on A LOT of production vehicles (Ford, Nissan, Volvo, Saab). They can make impressive power, but were known to be laggy.

The T04 family = "big turbo" that makes huge power, but is very very laggy. Without the beauty of being able to make a hybrid turbo, a T04 would probably not even be an option.

The 3 main components that have the biggest impact on performance are the a/r of the turbine housing, the size (aka trim) of the tubine wheel, and the size (aka trim) of the compressor housing.

Common turbine housing a/r "sizes"
T25: .64 a/r, .86 a/r
T3: .36 a/r, .48 a/r, .63 a/r, .82 a/r
T4: not listed...see why later

In a nutshell, the larger the a/r, the later the power comes. A small a/r gives you a fast spooling turbo but limits top-end power. A large a/r gives you a laggy turbo with big top-end power.

Common T25 turbines:
DSM trim (?? not sure how big it is, but it's quite small)
60 trim (small)
76 trim (medium)

Common T3 turbines:
Stage 1 (small -- most common turbine on junkyard turbos)
Stage 2 (med)
Stage 3 (large -- most common turbine on new T3/T04 hybrids)
Stage 5 (very large)

Common T04 turbines:
I'm not gonna list any because I don't have info on them and the T4 turbines require so much exhaust energy to spin that they are practically unusable in our application unless you want insane lag and have got a motor that will spin to 10k every day.

Common T25 compressors:
I'm not gonna list any. I do have some info on them, but for the most part, a T25 compressor will struggle to stay in its efficiency range on a boosted Honda.

Common T3 compressors:
40 trim (20lb/min -- haha...don't even think about it)
45 trim (21lb/min)
50 trim (30lb/min -- probably one of the most common on junkyard turbos, works well for SOHC and LS engines)
60 trim (34lb/min -- biggest "production" T3 compressor, excellent power on D series/LS)
"Super 60" (36lb/min -- note: this is NOT the "60-1" compressor)

Common T04B compressors:
S trim (37 lb/min)
V trim (48 lb/min)
H trim (49 lb/min)

Common T04E compressors:
40 trim (36 lbs/min)
46 trim (41 lbs/min)
50 trim (47 lbs/min)<-- awesome turbo for us sohc's (CivicRyda2k)
54 trim (45 lbs/min -- note that the 54 trim flows less than the 50 trim)
57 trim (49 lbs/min)
60 trim (50 lbs/min)

Common T04S compressors:
60-1 (flows a shitload, never seen a compressor map for it)
62-1 (bigger yet -- I believe this is a T04S compressor...correct this if it is wrong)


Performance (listed in order of increasing performance):
A T25 is a straight T25 turbo --> T25 turbine + T25 compressor (GT25 is similar)
A T28 is a hybrid T25/T3 turbo --> T25 turbine + T3 compressor (GT28 is similar)
A T3 is a straight T3 turbo --> T3 turbine + T3 compressor
A T3/T04B is a T3/T04B hybrid turbo --> T3 turbine + T04B compressor (used in Drag kits)
A T3/T04E is a T3/T04E hybrid turbo --> T3 turbine + T04E compressor (more performance than T3/T04B)
A T3/60-1 is a T3/T04S hybrid turbo --> T3 turbine + T04S (60-1) compressor"

*quoted from another board.. thanks!*