Are you an ebayer? I've found some really fantastic deals on there! I hate buying cheap stuff that falls apart but I'm no millionaire so I compromise by finding good quality at a good deal!
Breeches- The best brand is what fits you best! Side zips are still the most popular. Greenish beige is popular but there's a lot of more khaki/beige out there too. My favorites are Ariats, mainly b/c Tailored Sportsmans don't fit me. I have some higher end TuffRiders, Equine Couture, and RJ Classics that I show in as well.
Ratcatchers- Most brands are clearancing out their 100% cotton for coolmax. Definitely a worthwhile substitute! Colors/plaids/stripes are much more popular then they were in years past in the hunters but white is still correct for equitation classes. (although the most popular for white shirts is to have a fun lining for collars and cuffs) A new trend are "wrap collars". Instead of a detachable collar it's all attached and buttons together. They're new enough that I haven't been able to find any on ebay though! I haven't seen stock pins in years, mainly b/c they're dangerous! Monogramming collars has taken their place. Essex/Beacon Hill are my favorites. I have some Ariats but they're a little boxy.
Jackets- Almost all jackets these days have patterns (plaids, pinstripes, etc). Navy is always classic. But medium to dark grey is extremely popular, along with black (black with a pattern, not solid black), and the occasional brown. The most important thing about the jacket is fit. Not every brand fits every body type. Buy whatever fits you the best! Grand Prix are good quality, as are Tailored Sportsman, Ariat, and RJ Classics. But out of all those the Ariats fit me the best.
Helmet- whatever fits your head the best! (noticing a theme here?
) Fora while in our area GPAs and Charles Owens were neck and neck for popularity and I think CO's finally won out. (at least in the hunters). They have several models that fit differently so it's worth trying them all on. I see a lot of IRHs at the local shows.
So the common them is buy what fits! :) hope that helps a little bit! It can be overwhelming to have to find all of that stuff... but very fun too! Have fun with it!