Having attended 60+ games over the past 3 years, and having sat almost everywhere in PacBell, I would recommend the following:

If you have the coin, go for $28 lower reserved seats. Close to the field, but not as pricey as the $38 field club seats a few rows in front of you.

If you are looking for a good value, go with View Box (first 3 rows on lip of 3rd deck) or Arcade (right field), both of which offer good value for $23.

Club Seats are overpriced at $38 and not as nice as Field Club but you do get nice concessions. Whatever you do, avoid upper reserved at all costs - these are $19 nosebleed seats and you will be kicking yourself for not paying a few $$ more to upgrade.

Best place to find advance tickets (often at face value or less) is www.craigslist.com
Avoid the Giants official ticket site as you will pay ridiculous service fees for crappy seats (the good seats have already been sold to the 30,000+ season ticket holders). You can also find plenty of good seats for face value or less being hawked outside the stadium on gameday, even cheaper for night games.