I have a Palm Tungsten T and I'd be so lost without it. It's so much better than carrying around a bulky planner.
The best thing, though, is a program called Vindigo which you can download at
www.vindigo.com for $30-some per year. Basically, it gives you restaurant, shopping, and entertainment guides plus maps for all major US and international cities. SUCH a huge plus when I'm out on the road for work and want to have some fun!