Where are good places to buy pre-built circuits?

[martianviking]

A few people (such as GameSX member "matt") have mentioned the option of buying ready-made versions of some simple circuits rather than building them.  I will probably be building my own, but if I change my mind (or if someone reading this doesn't have the time or skills), where are good places to buy simple pre-built circuits?

The type of circuits I am talking about are 3.58 MHz oscillators (for building RGB to NTSC encoders), adjustable attenuators (for converting speaker level audio to line level audio), and similar such things.

Any suggestions for sources?

[Lawrence]

Why would you want to buy a speaker level convertor kit when you can buy a high-quality adaptor in a production shell for $20-30?  How cheap would you have to be to think that's too much money?  =P

[martianviking]

Pretty cheap.  You'd be surprised.  

Seriously though, when people say, "If you don't feel like making your own oscillator circuit (which is very easy), you can buy ready-made ones for $2-3," I start to think that it might not be such a bad idea.