The Continental Presidential Plus credit card from Chase mentioned upthread is probably a better deal than purchasing United Club membership directly. It has a $395 annual fee minus a one-time $95 credit after first card use. Includes a full United Club membership, including guest/family privileges, plus a few other benefits like United baggage fee waivers and EQM earning.
The American Express Platinum card ($450 annual fee) includes a Priority Pass Select card (good for lounge access for one person, although not for United Clubs), up to $200 in airline fee rebates, and several other benefits. That card also gets you into American, Delta, and U.S. Airways lounges.