Check out Acer ... they are awesome machines, and very well priced to boot!
Dell's have a worse rep than they really shoud for some reason. I have business clients who are entirely Dell outfits. Not a single problem on the desktops! Laptops, well that's another story, personally I always go Toshiba if I can ... worldwide warranty is awesome. Fuji and Acer would be my next choice, not much after that. One thing Dell's do have is that their cases are awesome! Screwless, and a joy to work in. Upgrading is a cinch as long as you don't mind paying a little extra for RAM.
I might be wrong, but I believe that Dell use re-branded Intel motherboards in a custom layout. If this is true, then I can say Intel have some totally rock-solid boards that blow away the likes of ASUS and ABIT.
As far as custom built machines ... they aren't always best. I see a lot of custom machines that are just plain 'wrong'. Cheaping out on certain things, and going overboard on others. The biggest problem with custom built is that people get their information from guys on gaming forums ... hate to offend anyone who is that type of guy, but I would personally rather let a monkey build a machine for me than some of those guys. I've read enough threads from people who's "awesome" cooling tricks actually go against the pricinples of air cooling and the thermal dynamics of cases. There is a LOT of misinformation on those types of sites, and hence PC builds aren't as good as they could be. Personally I would always be wary of someone who calls themselves a 'system builder' because they can plug a card into a PCI slot, there's a lot more to it than that ... afterall how many guys on this board would call themselves a mechanic just because they can change oil and filters!
Don't get me wrong, a lot of custom systems are great, but there is a lot of mis-information that you can follow.
Any way ... check out Acer systems, rock solid and 3 year warranties as standard.
