As low end machines go, you really can't beat an Emachines. After being a die-hard BYO user/builder for years, when both of my computers were stolen and I needed a replacement rig in less than 24 hours, I bought one for what I thought would be a temporary solution. Needless to say, one year has passed and the Emachines is my primary network hub/general use computer. Here is what impressed me about them:
1. Quality off the shelf parts. The mobo is N-force based and the HD is a Western Digital.
2. Adequate RAM. Came with 512mb DDR
3. Respectable documentation. In addition to the quick start manuals that come with every rig, they included a manual for the mobo for both troubleshooting and expansion options.
4. Software suite. The hardcore wont use it, but for people who dont really know what they are doing, the starting software package can help them out even with their computer problems. They include something called "Big Fix" which notifies you if you have gone too long without a defrag or other maintenance tweaks and how to do such. Additionally, the standards such as MSWorks and Money along with Roxio are included.
Another company that I recommend is PCClub. If anything, it is not for their prices. It is because of their service. When I found on a more recent rig that I bought from another vendor, that they forgot to include the O/S disks, I went to them (PCClub) and asked how much a copy of XP would be. Rather than selling me the OS, they told me that if I could bring in my comp and had my own software key, they would loan me the OS and make me a copy of the CD onsite provided I stayed onsite with my comp to do so and did it myself. The units they do build are respectable with plenty of room for whatever you need.
www.pcclub.com
High End Machines - Personal experience tells me to go Alienware or Falcon-NW. However, with Alienware having more proprietary mobos in some of their units, I might shy away from them.
Machines to Stay Away from - That prize goes to both HP and Dell. HP was the vendor that sold me the unit without the OS disks. It took a local TV news consumer report for me to get the OS after I had fought with them for 5 weeks.
Dell on the other hand comes from word of mouth. Two of my friends ordered Dells through the military discount program. The custom machines they ordered were not the machines they received. After 5 returns, they got the product they ordered, but almost a year after they ordered it. Additionally, initally, it took more than 3 months to process the orders. Both friends were stateside. I heard other horror stories from other military members, and as a result, will not be purchasing Dell, even if the overall satisfaction is considered satisfactory.
I hope this helps.