With the right pump and a large radiator, it is true that you can have a completely silent PC. A fan is not required if you use a large radiator, one that can handle the heat load passively. There are drawbacks to this, however.
Here are a few tips I think will save you time and money when getting a WC setup.
1. Decide if you want silence or performance, or a happy medium
2. Decide if you need to move the setup (ie. will it be external or internal)
3. Determine your maximum allowable budget... and plan on spending at least $20 on small things you didn't think of.
4. If you want silence, Eheim pumps are very good, as well as Iwaki, which are more expensive. A good, quiet pump is the Eheim 1250, very popular too. If noise is any concern at all, avoid Aqua Via.
5. The best cheap radiators are heater cores, and it is easy to find a heater core to fit your needs
6. The waterblock is actually not important as you think... most modern blocks perform very close to each other. It is better to consider the cost and clamping method when buying one, rather than performance. Besides, 90% of waterblock reviews are utter garbage, do not trust their numbers.
7. Where to buy on the cheap: Ebay for pumps, Auto store/junkyard for heater cores, FS/FT forums for waterblocks.
Generally, even decent watercooled setups are better than the best aircooled setups. It is possible to build a silent watercooled PC that performs better than the best, loudest HSF.
Check out the articles at overclockers.com and procooling.com, these will certainly provide some inspiration.