It's sort of a pick-your-method kind of thing.

ULers will get drops or tablets like Micropur, or nothing at all. I know too many people who've lost weight, time at work, and money treating giardia to feel good about trying my hand at developing good water source judgment and just take a Hiker Pro, taking care to lob it in the footbox overnight if it's going to be in the low 20F range.

Most of the filters you'll find at REI or similar - MSR, Katadyn, Platy Cleanstream, Sawyer - will do the job nicely for bacteria and cysts, the main concerns in continental US backcountry. (Platypus and MSR are branches of the same company, Cascade Designs, so the gravity filter units are actually the same thing in different colors.)

Iodine has been found less effective against giardia by the CDC and can be a health hazard in itself. Chlorine dioxide, which is used in Micropur and other chemical treatment methods, is more so. Some people combine chemicals with a cheaper filter like the Frontier Pro (which only gets the biggest of the microscopic pests) because treating for cysts with chemicals means a long wait time - the chemicals get the small stuff in 15 minutes or so, the filter gets the big stuff in the time it takes to filter.