In reply to tony: There's two GPS watches with barometric altimeter - the garmin fenix and the suunto ambit.
I have both (sad, I know), but am currently using the Suunto.
Reasons:
Customisation: I can change the fields for each activity, and add and subtract as many as I want. You can also construct "apps" to measure what you like (so for example in the "track running" activity I've added a field to show me my pace per 400m, so if I'm intending to run 90 sec laps I can keep an eye on pace)
Button presses: it sounds daft but the Garmion requires quite a long press on the lap button, which if you're doing hard intervals you don't want to do.
Looks: I like the look of the Suunto better
Updates: Suunto have a track record of providing regular, meaningful updates to firmware, whereas garmin tend to be pretty good in the early days (usually fixing bugs) but then move onto the next device.
Movescount: I quite like the Movescount website that stores "moves" and allows to use other users "apps".
Movement detector: The Suunto has a motion detector and the Garmin doesn't - that doesn't matter to me at the moment, but they could use this to track swimming activities with a software update.
However, the Suunto's not perfect - it doesn't have an auto-pause, which is a pain. Garmin has a much cleverer ski racking mode that can recognise lifts (and auto laps on them). The Gramin has better alarms - you can set a Mon-Fri alarm, and have multiple alarms as well. The Suunto doesn't have a vibrating alert, which I like on the Garmin. And finally Strava doesn't work directly with Strava - you can import tracks but it's a two step process.
So at the moment I'm keeping both, but I may be selling the Garmin at some point! For seriously in-depth reviews check out dcrainmaker's site.