I’d like to get a simple piece of software for monitoring my Internet
connection and recording information such as average latency to
various sites and transfer speed (ideally upload and download).

Requirements:
+ Windows 2000 (or later) application
+ Shows graphs of performance over user defined periods of time e.g.
what was the average latency every day last month.
+ Customizable performance tests (e.g. time interval)
+ Easy to install and set up

Would be nice:
+ Price is less than $100 (but I’d be interested hearing about
software over $100, too)
+ OS X version (either the same software, or something for OS X that
works, too)

Hiya MrFrog, 
I've always stuck by ping plotter (www.pingplotter.com). You can run
multiple instances of it, get averages and also bitmaps of traffic. As
for Transfer speed try
http://www.pcpitstop.com/internet/bandwidth.asp, admittedly its not a
program but it may help. If you are going to use pings as a measure of
latency check out this
http://homepage.ntlworld.com/robin.d.h.walker/cmtips/traceroute.html#traceroute
for some warnings.

Hope it helps.

Have you checked out MRTG.  See
http://people.ee.ethz.ch/~oetiker/webtools/mrtg/  It's free under the
terms of the GNU general public license.  It's primarily a tool to
monitor traffic loads but due to the amount of contributors to it's
development there are numerous add-ons for it to monitor just about
anything (that has SNMP support).  There are also many many people
available to help if you get stuck.  Unfortunately there is no version
for Mac (Unix and Win32 only).

Hope this helps

Darren

Hope these help - 
You may also want to check out the products at VisualWare
(http://www.visualware.com/products/index.html).  They make a variety
of programs that track numerous performance measures (latency, web
performance, etc.).  I have used their products at work and have found
them easy to install, use and they are priced competitively.  Only one
of their products - VisualRoute - works on the Mac platform though.

MRTG is also useful, but would require more configuration, although
depending on your time available and your technical aptitude, that may
be preferable to spending any money.

If you want software over $100, I would recommend looking at What's Up
Gold from Ipswitch (http://www.ipswitch.com/Products/WhatsUp/index.html)
or Solarwinds (http://solarwinds.net/Toolsets.htm).  We use Solarwinds
at work and i found it easy to setup (it really does take about ten
minutes if you have the IP addresses of the devices) and begin
monitoring.  It may not be exactly what you are looking for.  What's
Up Gold retails for about $795 and the Solarwinds packages range from
$145 (Standard Edition) to $995 (Engineer's Edition).  Both of these
products allow 30-day evaluation versions to be downloaded from their
web sites.