Sidney, "What is a good server brand and model?" is the wrong
question. Tell us what your goals are for this server, what software
you want to run, how many users you want to support, etc., and someone
can give you a reasonable guess about what hardware you'd need.
Apparently you want to run Dspace and dotLRN - that's a start, tell us
more.
In all likelihood, pretty much any modern server would be
adequate for your OpenACS/dotLRN site. For instance, openacs.org runs
on rather old and modest hardware. For many users, a $600 box from
Dell is more than enough. But then there are also some OpenACS
installations supporting tens or hundreds of thousands of users on
massive 4 or 8 CPU SMP boxes. It all depends on what you're trying to
do...