Let's be real, as your mileage increases, so does your cycling gear. When I find places to buy from, here's what I keep in mind:
1) If I need to return, how easy is it to return an item (pre-paid shipping label, drop off location is accessible, etc.) - Especially for higher end stuff because a comfortable fit matters a lot! I'll sometimes order 2 of the same things in different sizes and return the other one (ex. helmets and shoes).
2) If I know what I want, I compare the price/shipping time against each other.
3) What's their shipping cost like? Is there a minimum in order to get free shipping?
Here's a list of reputable cycling websites to scope out and start stocking up for your future adventures:
Competitive Cyclist - online only - carries a variety of apparel, accessories, bikes, nutrition
Wiggle.com - online only- similar, based out of the UK, surprisingly has cheaper stuff than US based companies (even with shipping).
Chain Reaction Cycles - online-only - carries a variety of apparel, accessories, bikes, nutrition.
Jensonusa.com- online-only -carries a variety of apparel, accessories, bikes, nutrition
Performance Bicycles- online only - carries a variety of apparel, accessories, bikes, nutrition.
Decathlon.com - online + physical store - With an international presence, this store is fabulous for people who are just starting and want to explore an athletic activity wherever they are with a low investment. The prices are hard to beat, worth giving it a shot if you're curious!
REI.com - online + physical store - US based brand. If you have a membership with them, you can try out items and return them within a year if you don't like it. They also has a plethora of equipment for other sports. Since it is a retail store that supports nearly all things outdoors, their cycling section is also worth looking into as they carry some popular cycling brands.
Amazon.com - online only - basically, the everything shop. I also use this to compare prices and order items that I can get the next day with Amazon Prime.
There are a ton of stuff and brands out there and overtime, you'll come to know which ones suit and fit you best. Bring out that personality with clothes jerseys and socks :). If you're looking for bike components like cassettes, gears, pedals, etc, I recommend spending more time on research prior to investing to make sure it is compatible with existing parts on your bike. Stock up on inner tubes if your wheels have that. Buy what you're most comfortable with purchasing and experiment with other items/brands as your bike closet evolves. You'll have struck gold when an item just fits you (and/or your bike) like a glove!
I'd love to hear from you - what websites do you frequent to stock up or explore cycling gear?