My "new" server is, again, Apache 1.3 but using SwitchPipe ( http://switchpipe.org/ ) which is a lot more reliable as it manages the mongrel and thin processes I am using. However, in the future I anticipate I will move to Phusion Passenger ( http://modrails.com/ ). I am starting to use SQLite3 more in apps. It's "fast enough" for small sites.
I used EV1Servers (now The Planet) for quite some time, but now am a SoftLayer man!
We do service monitoring and control via monit, deploy via Capistrano, and run a custom source-built Ruby distribution from a network share mounted on each of the app server boxes.
I'm watching mod_rails/Passenger with interest, and once it seems to have stabilized a bit, will probably try it out for at least some of our apps.
Slicehost is really popular and with good reason. Linode might turn out to be just as good, but I know the wonderful service I have gotten at Slicehost and how many other sites in the web 2.0 community are there - heck, the Xen blog itself is on Slicehost and not any other Xen provider.
mysql for data
memcached for caching
sphinx for search (ThinkingSphinx plugin)