I agree with most that by far the best mountain bike ever created was the GT Xizang, a hardtail titanium-frame mountain bike. Exceptionally strong, light weight and durable. Corrosion proof, if you're considering rides along the sea shore. GT went broke (probably from putting too much quality into their products for the price) and so the only titanium Xizangs you will find are resale market. There's on on ebay right now...

http://cgi.ebay.com/ws/eBayISAPI.dll...#ht_500wt_1284

I'm NOT the seller, and don't have a clue who the hell he/she is. I just follow Xizangs as they come around. If an 18-inch (average size) would work for you, this is the bike that will last you the rest of your life. And your children's, and your grandchildren's...