These threads always get a varied amount of replies. So far you've been recommended everything from a Rolex to a Timex.
If you're on a budget the Rolex, Omega and other designer brands aren't going to be something you'll consider. I'm figuring your budget is less than £100 so basically that leaves you with Casio, Timex and one or two Citizen and Seiko models.
Everybody has their favourites and there's a mixture of taste and functionality. Some people's favourite watch might not be the best outdoor model but they find it aesthetically pleasing. You didn't mention your personal preference, digital, analogue, combo, mechanical, electronic. Solar power, battery power, automatic.
Personally I always wear a watch but I've no great love for them. One watch is enough for me and I wear it for every occasion. For me a good outdoor watch needs to be cheap enough that I won't cry if I break or lose it. Rugged enough that it takes a lot to break it - shockproof in other words. The time should be easy to read and visible in the dark. It should be waterproof. It should be comfortable on my wrist with a strap that is both easily adjustable and not too fussed if its dipped in muddy water or other slime.
Other features that I look for are: A sunken bezel; raised bezels scratch quickly in the outdoors and get cracked. Buttons that are recessed with little or no chance of being ripped off or adjusted accidentally. The old fashioned knurled knobs that stick out of the right hand side of many watches get caught on branches and other things and adjust themselves or break off.
So far I've broken every watch I've ever had except for an ancient dirt cheap Casio that was so naff that I got fed up of it and gave it away. In the past few years I got through two Timex Expeditions. They weren't expensive so they aren't a great loss but it was annoying that they broke so easily.
I decided to switch loyalty and I bought a G-Shock after much deliberation. The entire range is well suited to the outdoor life and it is reasonably priced. They are well thought out with regards to taking abuse. They might not be the prettiest watches around but they are functional and they look okay. If you do manage to break one you'll be out by around £40-£100 depending on the model.
There's a choice of atomic timekeeping, solar power, analogue, digital, ana/digi, battery, long life battery, fashion style or classical style. The more expensive Protrek watches are similar and might be worth looking at too.
Here's the current G-Shock line up for the European market:
http://www.g-shock.de/euro/lineup/
Mine is the AW-591MS, one of the few models with a cloth strap (something I personally like for several reasons). I'd recommend the model I bought because I'm pleased with it for the price but design and features are down to personal preference. I'm not recommending these watches for their aesthetic appeal, high price, snob value or collectability but as a decent tool that can take abuse and not cost a fortune.
Here's an abuse test for you:
http://forums.watchuseek.com/showthread.php?t=57302
I'm not expecting my watch to suffer like that but it's good to know that it can.