Small pickup trucks seem to be generally overbuilt and robust. From what I've seen, they don't break all the nickle-and-dime stuff that fails on most cars and they're fairly simple.
I'll second the 60* V6 recommendation. It's a tough engine (so long as you don't rev it to redline every shift) and easily replaceable and upgradable.
The 4.3L-powered S10s can absolutely fly, but the engines tend to be less reliable. You'll also be tempted to drop in a Chevy V8. Don't do that.
If you're not partial to brand, a four-cylinder Ranger with the old Ford Lima engine should be pretty reliable. For Fords, cylinder count and displacement seem to have an inverse relationship with reliability.
Eric Rood
Everything Bagel, 24 Hours of Lemons
eric@24hoursoflemons.com