It really depends on what you need.
If you are looking to mask your traffic at Starbucks or a hotel there are a number of free options that are fine for occasional surfing/email use. On the other hand if you are looking to mask your location (to get a geographically restricted service, for example) or you are consistently on the road working out of hotel rooms I'd recommend ProXPN. Their connection is solid, you get decent bandwidth and you can terminate in a number of countries.
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