I've been a Dell devotee since 1998. And have been converting towards being a completely Dell shop. So I suppose it would be your preference. Shop around, get some reviews, basically do your homework.
Now, I was just at Dell's website, and they offer a really scaled PowerEdge tower at about $699 on up to $1,890. You can customize your hardware configuration configuration and even select which network operating system to have installed Windows Small Business Server 2003, Red Had Enterprise Linux v4 or SUSE Linux Enterprise Server 9.
http://www1.us.dell.com/content/products/compare.aspx/tower?c=us&cs=04&l=en&s=bsd
I have had experience in the past with Gateway and IBM, but felt their tech support was far less superior than Dell's tech support.
As I said earlier, shop around, do your homework, research reviews, and compare costs.
DISCLAIMER: This is just my opinion on Dell! And I'm biased! ;)