I was annoyed that McMaster didn't give me a shipping total the last time I ordered from them, but UPS ended up being less than I expected. They really have an extensive catalog and their website is pretty good too.
They have an enormous selection, I use them constantly at work.
+ Ridiculously large selection
+ Fast shipping (mostly next day)
+ Rarely anything out of stock
- Often on the expensive side, especially for raw stock
- They don't list any manufacturers, so you're never sure you'll get the exact same product when you reorder
- Shipping isn't calculated at checkout