Obviously this is going to be slightly biased no matter who's telling you, but here's my top 3 for every category, best on top:
PSUs:
PC Power & Cooling - Best quality, but expensive
Silverstone - Reasonably price, still excellent quality
Antec - More budget, but still good
Fans:
Vantec - Good quality, Tornado moves a TON of air
Basically whatever's cheap with good CFM
Mobo's:
Abit - Top quality
Asus - Only complaint is extremely slow website
DFI - Great for overclocking, enthusiast boards
HDD:
Seagate - Best reliability in my experience
Western Digital - Raptor is awesome
Cases:
Lian-Li - Best by far, not cheap but the build quality is amazing
Cooler Master - Not bad for a budget
Overall Cooling:
Thermalright - Ultra 120 Extreme is the best CPU HSF
Tuniq - Tower 120 is also very good
Arctic Silver - AS5 is great thermal paste