I've been using Ruby at work to write watir tests, and I am constantly amazed at how elegant it is. Here are some of my favorite techniques:

Pass a default value block to Hash.new to implement a memoized recursive function:

fibonacci = Hash.new do |h,k|
    h[k] = k >= 2 ? h[k-1] + h[k-2] : 1
end
0.upto(100) { |i| puts fibonacci[i] }

Use an anonymous array to perform some operation on a constant set of things without repeating yourself:

['golf', 'baseball', 'hockey'].each do |sport|
    play(sport)
    stopPlaying(sport)
end

Instead of:

play('golf')
stopPlaying('golf')
play('baseball')
stopPlaying('baseball')
play('hockey')
stopPlaying('hockey')

Use an anonymous array to check of some variable is equal to any of a set of things:

raise 'Invalid sport' unless ['golf', 'baseball', 'hockey'].include? sport

Instead of:

raise 'Invalid sport' if sport != 'golf' && sport != 'baseball' && sport != 'hockey'

Initialize an array using a range and map, and use rand() with to_s to generate random strings:

randomStrings = Array.new(100) { rand(2**64).to_s(36) }
users = (30..50).to_a.map { |x| "testUser%d" % x }