The other day used my brother Ithlete app. Pretty cool. Basically a cheap man's OMEGAWAVE substitute. What it does is gives u a reading of" readiness" by giving resting heart rate and most importantly Heart Rate Variability(HRV)
pretty cool, as i mentioned above, one of the main functions of an OMEGAWAVE is measuring HRV.(think mine was 72 that day, below 50 is an indicator recovery is needed)
obviously this isnt something that is a MUST in training, but IMO definitely a valuable asset
as my brother phrased it "it tells me whether i feel sluggish and not like working out because I am worn out and not fit to train, or simply because I am being lazy"
I think totally cost is 60 dollars or so (not including heart rate monitor) 50 for equipment for iphone/ipad +10 for actual APP
more cool APPS out there everyday
heres the info about it
http://www.myithlete.com/ithlete-lowdown/