There is an interesting mix of cycling computers with GPS and watches with GPS out there. One that seems to be popular for bikes is the
Garmin Edge 800 and I like that it actually has a visual readout screen like the full sized car GPS units. The price for these seems to hover around $300 so to Chanlee's point, I think you might want to weigh the pro's and con's of using a purpose built GPS that might be limited to your bike or a smart phone that could do all kinds of neat stuff (but might require a data plan).
There are some pretty reasonable data plans these days and you can get inexpensive Android units used or online for under $100 that will run Google Maps. Virgin Mobile has a $35/month plan with unlimited data, web, messaging and email and you can get a Kyocera Event from them for $39.99 but then you might have issues finding a good mounting kit. I personally like how the iPhone works and know there are a ton of cases out there for it.
Here's one scenario: get a used iPhone 3 on eBay for $99, figure out which network in your area will actually be able to provide decent data coverage (so you don't get lost and stranded when it doesn't connect) and buy a mount like this one on Amazon called the
Perfect Fit Bike Mount and this way you'll have GPS and a way to call for help if you get stranded or have an accident with your bike.
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An alternative might be to just buy an old car style GPS off Craigslist or eBay etc. and then charge it at your house before using. This would not require a data plan but you would run the risk of battery failure. My old Garmin GPS is awesome and still works well (you can even pay $100 to update the maps) but it doesn't offer bike routes like Google maps does, it doesn't have traffic (though a new Garmin might) and the battery fails pretty quickly and is not easily replaceable. I saw several Garmin NUVI units on eBay for < $50 and they have the larger screens and look pretty nice.
Do any of these sound like decent options Icthus or are you looking for something different? I haven't used the simpler monochromatic GPS units or watches so admittedly my feedback is skewed towards the fancier stuff here.