A favorite source for many of us is

Crutchfield Audio

Use the vehicle selector. Many popular and specialty radios to choose from at good prices and with an excellent reputation for customer service. If you find a model you like, google search that model number just in case somoene else, like on Amazon, has a better deal at the moment.

You will likely need to add to your purchase a dash kit consisting of a single DIN height mounting adapter and a suitable face plate bezel, as can be found with the vehicle selector.

For most standard applications, I'd recommend you get the associated plug&play wiring harness adapter from Crutchfield at the same time. Saves a lot of effort, but you can butcher up your existing harness and the new radio harness to splice them together if you want to save a few bucks. You would then need to know the wire colors and connector pin numbers. There are some here in the FAQ and others that google may be able to find. If needed, post back and someone may have the proper wiring diagram for your year.

I can't remember if your 740 has a separate pre-amp, some did, so if it does then you can get a radio that uses an external amplifier, otherwise just get a standard radio with a built in amplifier and disconnect the wire harness for any pre-amp that may be under the dash.

Once you get past MP3, USB, CD, iPhone, handsfree Bluetooth, satellite radio, etc. connectivity features, it's mostly a matter of deciding how wide you're willing to open your wallet in relation to your speakers and audio tastes. Once you get past the cheapest radios, speakers quickly become the limiting factor in listening quality. Lots of consumer reviews out there to help you.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now