Rackspace is the leader in dedicated hosting and is fanatical about customer service. Hosting with Rackspace is pricey, but is worth it for mission critical sites with high volume traffic.

Crystaltech offers shared and dedicated Windows plans, and dedicated only Linux plans. The pricing is competive and reasonable and their customer service is excellent given the price. Their dedicated plans are fixed configurations, with no customization available. Great for basic dedicated hosting, but if you need a custom server, they don't offer that.

We like AN Hosting for shared Linux plans. The prices are great and they continually get rave reviews for the speed of their servers.