I use a Maha C204W for $40 that has no wall wart and accepts a variety of input voltages for use while travelling. The C204W is similar to the C204FA, but the C204FA is cheaper at only about $26. Like the C204W, it cannot charge just one battery at a time: you have to charge them in pairs. I like it because it charges quickly and packs more charge into the cells than other chargers in that time. Most chargers need overnight to trickle charge the cells to pack that much energy into the batteries. This charger also has a battery conditioning mode to bring capacity back to old cells.
For around $20 you could get the Maha 204GT. It takes 3-4 hours to charge, but similar to the two chargers I mentioned above, it attains a more complete charge compared to other chargers without waiting overnight. It also charges only pairs of cells.