[fredjacksonsan]

I'd beware of one that was heavily modified. I'd stay away from '99 or '00 models with the 4.0 Liter...those years used substandard metals for the head and it will develop invisible cracks allowing coolant into your oil. (Do a search for "0331 head" and you will find a bunch of information)

Otherwise, Wranglers are usually very reliable. If you choose an automatic transmission, change the fluid every 30k or so. Follow the recommendation for oil change intervals and other fluid changes. The 4.0 engine is great, but change the plugs every 30k as recommended and you'll be better off.