The best 'convenience' charger for li-ion cells right now is probably the Pila charger, but it's fairly pricey, about $50 US from most online sellers.
I use an Ultrafire WF-139 which works fine for my purposes. I always use protected cells, and I've never had a problem with it, but I have read that if you aren't using protected cells, you need to monitor the charge in the cell with the WF-139 because it can overcharge unprotected cells which will make them very unsafe. The Pila is supposed to have its own termination circuitry so you can use it with unprotected cells with a bit more leeway in terms of how closely you have to monitor them so they don't overcharge.