not sure how many providers there are actually
i switched from comcast cable to clearwire
and clearwire is good enough for internet but it is alot slower for uploading and downloading
i was triiing to upload a wedding on my smugmug site and i had to give up and go to a freinds house that had comcast
so if you need it for major stuff i would stick with cable
but clearwire is super easy to set up
basically right out of the box and boom
ready

As for WIRELESS providers I am assuming you mean something along the lines of Cellular or other portable, transportable providers.

Your options these days are primarily the big carriers (assuming they have full coverage in your neck of the woods.)

The main wireless Internet providers are:

Verizon - Full 3G EVDO network, you will get speeds up to about 700Kbps through a handset or you can get supposedly up to 1.4Mbps if you use one of those EVDO MoDem things for your laptop. (Also best coverage if you want a service provider that will work in the most places.)

Sprint - 3G EVDO as well, I do not know too much about it since I have not used it, I would assume that it is on par with Verizon, I know they are definately faster than the other carriers except Verizon

AT&T / T-Mobile - Both are running on GPRS/EDGE maximum speeds are around 200Kbps (I hear you can hit about 400 in some places.) (Part of why I will not get an iPhone, it is too slow.) AT&T is supposed to be upgrading their back end to 3G technology which will mean in the future they will be able to offer speeds aproaching 1-2Mbit, but it is not there now.

Local other carriers, in different areas you will find some regionalized carriers such as All-Tel that offer said services as well. If you only plan to stay in your local area not travel much they are a very viable option, but not a good choice if you plan to have stable access throughout the country.

IF you are looking for Wireless Internet for your home/office there are several microwave/satellite companies out there as well:
The ones I know:

TowerStream - Microwave provider (they work with the smaller footprint transceiver antennas so they are easier to implement in more locations, you do not need a large bulky microwave dish on your roof.)

Dish Networks - Satellite DSS provider, decent speeds, but the upload usually suffers.

Hughes Communications - Satellite provider as well, offers much broader coverage area as well as some international coverage.

Something to note about satellite service, they run some crazy QOS's that really impeded on bandwidth usage. Unless you have a business, high bandwidth account you will have issues with downloads, also VPN's get a little tricky due to the latencies involved in satellites.

I hope this maybe helps a bit. There are a lot of wireless Internet providers out there, also on the local/regional level there are some other options like here in San Francisco they are working on this city wide wi-fi system which is only partially built out. Also there is another peer based system in some neighborhoods here as well.

Also in about 2 years Verizon & AT&T will be offering 4G wireless broadband for your home and to go when they start using the newly available 700MHz band.