You can get lower prices for hardware out of prgmr.com. I have used one of their VPS plans for ~6 months now, and had almost zero problems. The trade-off is support. While their system very rarely gives me issues, I have had them. And they were my fault and I had to fix them on my own. There's generally somebody on the other end of the line if I send an email for help, but the exchange would normally go something like "I'm getting this error from grub, but I can't track down the problem" "[reply with a link to the prgmr wiki, with an article that answers most of my question]".
But they tell you right up front that they aren't here for support. From their homepage:
- An easy to understand price schedule: $4/month per account, and $1/month for every 64MiB ram. Please note; this means all plans come with $4/month worth of support.
Their slogan is also "We don't assume you are stupid."
If you have your configuration down to a science, and you know what you're doing in the shell, you shouldn't have any issues. They've been completely reliable for me since I got my configuration issues ironed out (again, the issues were with my setup, not their VPS).
There are comparisons that show prgmr outperforming, in this case, Slicehost by a large margin at times. On the flip side, there are comparisons out there that show other VPSs giving higher performance with less hardware for the same price in some situations but have prgmr's performance holding very steady. So evaluate your needs accordingly.