It never ceases to amaze me how much good free tech there is out there (admittedly many of the products I'll be discussing here have expensive paid-for versions, however for a small business, most of these products meet our needs perfectly - and I'm sure you will find them worth adding to your toolbox.
Splunk - google for log analysis (free version allows you to throw 500mb of data at it on a daily basis).
I'm still trying to get my head around this product - looks pretty amazing from my limited use of the tool - allows you to index logs (and other data) from multiple sources, and allows you to easily search, create reports and build alerts.
Unfortunately I think the price tag is a bit out of our price range (I think it starts from $8000 US), however I'm sure that this is a bargain compared to CA Unicenter or Tivoli for larger enterprises.
For basic web server log analysis (specifically for Apache Tomcat) I have been happily using Webalizer for the last week. Nice and basic, comes recommended.
Citrix Xen Server - Enterprise grade virtualisation solution - make sure you evaluate this one, supports iSCSI targets, has a centralised admin console for your citrix xen servers, has support for dynamic instance migration (with shared fibre channel or iSCSI storage).
The free version represents exceptional value for money, the nice thing about this product is that it works on commodity "beige" hardware - whereas ESX has a limited range of supported hardware platforms (and drivers).
Spacewalk - this is the open source version of RHN Satellite server - we have it running with Centos 5.2, all our servers register with this service and patches are pulled down from the web into spacewalk "channels" and pushed out to our registered servers.
I believe it also supports the Solaris package management system (and Fedora of course). Centos contains the same packages (and more importantly, security updates) as Redhat Enterprise Linux (minus the $300US price tag). The packages are build directly from the RHEL source RPMs.
We have also registered an EPEL "Extra Packages for Enterprise Linux" channel for unsupported packages (think "Universe" for Redhat based distros).
Omnifind Yahoo Edition - free search utility - functionally this is very similar to the Google Mini Search appliance (which I purchased and used in a previous job) - it supports mounted SMB partitions and performs web crawling of local intranet sites - supports adding keywords (so that specific search results bubble to the top and synonyms).
The search syntax does not appear to be as sophisticated as the Google appliance, however it supports indexing the same content types and the free version allows you to index 500,000 documents (from memory we paid google $15k AU for this privilege).
The more money you pay, the more documents you can index and security controls are introduced.