I have a nasty sinus infection-it's been going on for weeks and causing migraines for days at a time. I took Levaquin, another antibiotic, for 7 days with no effect. We switched to Augmentin-a mix of Amoxicillin and clavulanate (spelling and accuracy?)-Amoxicillin is the main ingredient. This one works for me every time I need an antibiotic. It's not too frequently that I need something, but this year I've gone through this sinus infection thing twice now (I'll probably have to see a specialist because the last time it lasted for several weeks even with the antibiotics) and Augmentin worked both times for me. For this round of infection, I took Levaquin for a week, as I said before, then switched to this and within 2 days the infection has pretty much subsided. I'll probably be on it for a couple weeks since my history with these infections has been a bit impressive this year, but as long as it works I'm ok with it!
Side effects are similar to other antibiotics-it's almost guaranteed to make your stomach upset (the doctor gave me something for nausea because I'm super sensitive to stuff like this). It's a strong drug, so expect some pretty good side effects. As long as you can ride out those side effects, though, this is a very broad spectrum drug that will kill most every bug you could have.
One note of caution, though-Last time I bought this at the Osco pharmacy it was $20 more than at WalMart this time! Shop around for pricing!!