Just make sure the charger you get is appropriate for your battery. Correct voltage is obviously key, as is the charging current - the larger the SLA, the higher the charging current. Charging a small SLA with a very large current is a no-no. Powersonic provides a nice, easy list of which chargers are appropriate for which size SLAs.
The best chargers are "smart" chargers, or float chargers: they charge at full current until the battery is near-full, then trickle charge to maintain a full charge without frying the battery.
A couple online retailers (although your local non-RS electronics shop is probably the best bet):
I've been very pleased with the Powersonic chargers I've used. A little more expensive than the Xenotronic, but hearsay indicates they're sturdier and last longer.
Haven't used one, but haven't read any bad reviews.
Radio Shack (http://www.radioshack.com/
Has some cheap RC batteries and chargers.