I'm building my own computer for the first time and was wondering if anyone can suggest parts that are cheap but  people will still buy them. basicly I want cheap parts that work well. can some body please help me.

What do you want to do with this computer? Watch movies, gaming? Do you plan to overclock? How much are you looking to spend? How long do you want this computer to last you?

I plan to do a lot of downloading, watching a lot of videos and some gaming I also want this computer to last about 5 years or more. I want to spend as little as I can.

Okay. Let me make you a wishlist on NewEgg, and people can comment on it here.

What's your budget?

Do you need a monitor / keyboard or just the tower?

Are you scared to overclock?

Not my configuration, but a possible starting point:
http://secure.newegg.com/WishList/ [...] er=6593694
Grabbed if from effel on a diff thread

http://secure.newegg.com/WishList/ [...] er=6508434  
 
Tell me what you think.

I didn't mention this before but I also want to waste more money on the power supply because I want one that is efficient could you recommend one for me please. Also I like the items on the wish list you made thepowerofdonuts.

The case in my list is an Antec Earthwatts 500W. It's 80+ certified for efficiency.

thepowerofdonuts wishlist is a nice build. As he mentioned the PSU is an 80+ certified PSU. If ~900 is what you intend to spend, that is what I would recommend.

If you're looking to spend less, I can modify it, and there are mail in rebates in some of those items. I always look for those.

somebody I know told me that its better to buy a power supply that is separated from the case and I want a case that doesn't come with a power supply and I also want an efficient power supply what do you recommend.

Well it'll cost you more.
I reccomend any of Corsair's power supplies. They are single rail and very efficient.  
For the case, look at either the Antec 900 or the Cooler Master 690.