I've always liked the old designer's adage of "good, fast, or cheap, pick two". That is, a project can be completed quickly, it can be done cheap, and it can be done well, but you need to choose which two of those you want. If you want a good project done quickly, it's gonna be expensive. Fast and cheap? It's gonna suck. In his talk at SXSW, Jason Fried outlined another pick two scenario clients need to be aware of: "fixed scope, fixed timeframe, or fixed budget". Here are some more variations:

Elegant, documented, on time.
Privacy, accuracy, security.
Have fun, do good, stay out of trouble.
Study, socialize, sleep.
Diverse, free, equal.
Fast, efficient, useful.
Cheap, healthy, tasty.
Secure, usable, affordable.
Short, memorable, unique.
Cheap, light, strong.