There are many nice chargers on the market.
Here are the features I recommend you look for:
For micros: able to charge at 500 ma - 1.5 amps
For nonmicros: Able to charge at 3.5 to 5 amps
Delta-peak charge termination
Some type of false peak rejection capability (Sometimes called soft-start, peak delay, etc)
The soft-start/false peak rejection capability is especially important. Helicopters tend to discharge cells rather deeply, and when these cells are charged, the charger may often "false peak detect". This occurs because the cell chemistry is unstable when deeply discharged and the cell voltage will fluctuate randomly until the cell chemistry stabilizes.
A charger with soft-start or false peak rejection will not require restarting the charging cycle multiple times in the first 5-10 minutes of charging a deeply discharged battery pack.
The chargers which are known to fit these criteria are:
Maha MH-C777 Plus II (surface charge, Nicad, NiMH, Li-ion)
Great Planes Triton (peak delay, NiCad, NiMH, Li-ion, Pb)
Hitec CG-330 (false peak reject, NiCad)
Hitec CG-335 (false peak reject, NiCad)
Hitec CG-335 Pro (false peak reject, NiCad, NiMH)
Hitec CG-340 (false peak reject, NiCad, NiMH)
Robbe Infinity II (false peak reject, NiCad, NiMH)
Schulze ISL 6-330d (false peak reject, NiCad, NiMH, Li-ion,Pb)
Orbit Microlader (soft-start, NiCad, NiMH, Li-ion, Pb)
Orbit Microlader Pro (soft-start, NiCad, NiMH, Li-ion, Pb)
Orbit Pocketlader (soft-start, NiCad, NiMH, Li-ion, Pb)
The best value in chargers in this list is the Great Planes Triton. It has almost the same features as the high-end Orbit Microlader at about 1/3rd of the price.
Before buying a charger, make sure it can charge the number of cells in your pack! Some chargers can only handle up to 10 or 12 cells, which is insufficient for a Logo 16/20 or ECO 16.
This may be important if you're planning on buying a larger helicopter eventually.