Does anyone know of herbal remedies for giardia?

As much as I hate to say this, since I'm always siding against the "anti alternative medicine" people, you actually really should go see a doctor for this one. In my holistic health class, our teacher explained how he tried alternative cures instead of flagyl, got worse, and eventually had to use it anyways, at which point the treatment process was absolutely miserable compared to how he had felt originally.

That said, if you really can't afford to do that, there is an alternative. Giardia is an anerobic parasite, which means oxygen kills it. So, if you drink hydrogen peroxide, it has a good chance of clearing out the buggers from your body.
I have heard anecdotal reports this works, but I am by no means certain (whereas for a lot of other conditions I know it is correct to use and gets 90% success rates), since I haven't looked into it that much. If you plan on driking peroxide, ideally you want to buy food grade stuff online, but if you once again can't afford to, and only plan to drink it for when you have the parasites, it's not going to be a big deal (long term consumption of normal is bad because there are chemicals mixed in). Also, you need to make sure the concentration is not that high, ideally no more than .5% (which means dilute what you buy in the store). Through trial and error you'll get it.
Hope that helps, if yo.u want more information I can provide it.
*the teacher I mentioned at the start did not know about using oxygen therapies for this.

Not a good idea to fool around with these critters. Patient needs a course of metronidazole, an antibiotic for anaerobic bacteria.

Metronidazole aka Flagyl is a conventional antibiotic used to treat this problem with great success and minimal side effects, but as to herbal treatment, giardia is an intestinal parasite, so many of the remedies for parasites should be somewhat effective, such as garlic, ground raw pumpkinseed, wormwood, and probiotics.
Whichever treatment you use, you should see a qualified health professional and definitely follow up with a good probiotic and healthy diet. If you know where you got it, you should avoid that water source, or if it came from a pet, they should also be treated (dogs have been known to pass this to their owners).