Fenix Lights:
CE means Cree XR-E LED P4 unless specified. Go for the CE(Especially the Q5 versions, about 30% brighter then the P4 versions), Rebel 100(Better color rendering) or V2.0 models. They ave a more efficient and brighter LED. Twice or more output then the non CE, V2.0 versions.
The L0P, L0D, L0D-CE all use the AAA battery.
The L1, L1P, L1T, L1S, L1T V2.0, L1D-CE all use a AA battery
The L2P, L2T, L2S, L2T V2.0, L2D-CE all use 2 AA batteries
The P1, P1-CE, P1D, P1D-CE, P2D-CE all use a CR123 battery
The P3D-CE and T1 all use 2 CR123 batteries.
The L0Xes and P1xes are all twistie lights(Twist for on and off).
The LxT, LxS, and T1 have a twist(loosen) for low system.
The LxDs and P2D and P3D have a loosen for general mode(Low-Medium-High-SOS) and tighten for Turbo(Turbo-Strobe).
A full click or loosen(Form twisties) is always off.
The Digital series:
A tap when on or a quick On-Off-On cycle(Off has to be less then 2 seconds) will change modes.
Leave it off for more then two seconds and the light will reset to the first mode in the string.
Pretty simple in practice.
The P2D, L1D, and L2D(Doesn't matter if it is CE, CE Q2, CE Q5, Rebel 80, Rebel 100) all have the same electronics. Their bodies are compatible and with the same head, you get 1AA , 2AA and CR123 compatability(The P2D's tailcap is a bit large for the AA bodies and the AA tailcaps won't fit the P2D's body, but the bezels have the same threading).
The P3D and T1 are the only ones that can take 3.7v Li-ion batteries safely and not lose lower modes.
I think that's the whole Fenix line.
Fenix Store is in Atlanta Gerogia, has shipping included, and a 8% off coupon for CPFers, "CPF8".