if your just dealing with lipos the "ELECTRIFLY POLY A/C D/C CHARGER" IMO is the best bang for the money and will charge 4 bats ata time, some dont like it cuzz its not a high tech item with a big name but has worked well for me, Ive seen some used for $50
however if your just dealing with simple nimas the astroflight 110D is an excellent AC/DC charger as well, you can pick one up for around $35-40