I usually get my stuff from TradePac. I've also bought at least 6 rigs from them. Their prices are hard to beat in SLS.
I've gotta admit that I did have a slightly undesirable experience once with them when one of the mobos I bought was defective. I was lucky I was persistent and eventually got the mobo I wanted instead of the one they tried to sell me.
On another occasion, I was close to getting the Sapphire 5850 from them but I read in one of the threads here that it was supposed to be OOS, yet they claimed it was their last piece. Since I had prior knowledge, I was wary and checked the card before I even decided if I wanted to get it. The packaging was opened before and I was sceptical, so I decided to give it a miss.
It is important when patronising them that one knows what he/she wants to buy and is not swayed by their recommendations.
Do your research using the pricelists here or get bros here recommend rigs. Have a list of backup parts in mind, or be prepared to go to another shop if they don't have stocks for the parts you want.
My standard practice now, after buying so many rigs/components from them:
1. Take pricelist & highlighter.
2. Highlight parts you want to buy.
3. Pass to boss if he's around.
4. "Boss, gimme your best price" (be friendly and smile)
5. Don't haggle, boss usually gives his best price. I've been in retail, so I know how annoying it can be when someone asks for your best price, you give and the person asks for more.
*I usually pay at this point, but those who are paranoid probably can pay after checking the items*
6. Staff will get items for you, check against pricelist and check model/contents as much as possible.
7. Go home assemble.
I gotta say that despite some comments about missing accessories, etc, I've not had such an issue so far. I don't even check the contents very thoroughly usually. So if you know what you need to get, by all means buy from them and save some money. If you're new to DIY, try somewhere else I suppose.