Join Date: Aug 2012
Location: Auzeville-Tolosane, Midi-Pyrénées
Bikes: Redline Carbon Conquest Team, Colnago X-Lite (Wrecked, Stripped, Wal-Arted), Ibis Hakkalugi (STOLEN!!!), Bianchi Imola, Bianchi San Jose, Soma DC DC
Strava is free, and although a lot of the data feels very skewed, the times and averages are very accurate (in my opinion, using an iPhone 3GS, and comparing data to a Garmin 510 and to a Magellan CrossOver.)
Another nice thing with Strava is that you get to see relative times of folks in your area that make the same rides that you do.
Like a bike itself, performance-mapping can get ridiculously expensive. I would start with what you have and doing something for free and finding out what you like, don't like, and what things you'd want that you'd be willing to pay a premium for.
I have an old Joule from CycleOps that I got on eBay that I use with an HRM and a cadence meter. Then I use Strava and sometimes Cyclemeter (which is not free, but very cheap, $5-10.) For charting my performance over time, this overall package is fine for me.
I probably wouldn't even replace the 510 if it broke. My rides are less than five hours and my 3GS iPhone can handle that with Strava or Cyclemeter. I don't need exacting altimeter data. But I know some people love the data deluge. For me, I'm just happy with PRs or 3rd bests in Strava segments and moving up to 87th out of 260.