What are the top five companies that are providing enterprise level WLAN products and solutions?

I assume that you're asking about vendors rather than integrators. The Vendors are those companies such as Cisco, Enterasys, Symbol, Proxim, etc. (the companies that produce the products) as opposed to the Wireless Integrators of this world (Dimension Data, WFI, Simply Wireless, etc.) that sell the products to the general public whilst providing the services of integration to help you identify which is the best solutions for your company.

If we're talking about wireless vendors only, then we're heading into a very gray area with regards to "who has the best solution". A common misconception is that a wireless network sits at the edge of the network, commonly in a network DMZ (Demilitarized Zone), and is conceptually separate and physically isolated from the remainder of the network.

A more accurate representation would be to consider a wireless network like you consider your hand… extremely versatile, flexible and adaptable. However, much like your hand requires nerves for signals to be set to and from the brain to obtain the maximum efficiency, a wireless network must interact with the remainder of the network – interfacing with databases, RADIUS servers, VLAN configuration, QoS policies, network security intrusion devices, etc and as such there are very few companies that make an excellent end-end wireless system. In many cases the best end-end systems are 'best of breed' from multiple vendors.

Personally, when I think 'Wireless Networks' I only think about four different companies (and in this order).

1. Cisco Systems
2. Symbol
3. Orinoco
4. 3Com

I've looked at quite a few different wireless solutions over the years and using the above four I've found that I can satisfy almost anyone's technical requirements. To make it a bit easier I'll elaborate briefly on what I love about each of the different vendors.

Cisco – End-end enterprise everything. If it can be made to work and work well, Cisco does it. Cisco is the type of Vendor that due to their broad base and intense focus on being a market leader, their equipment will integrate ridiculously well with anything else that they make - meaning that you have MANY more features available to you than other vendors.

Symbol – Symbols latest product, their 'wireless switch' has taken the intelligence out of the APs completely, trunking all data from Access Ports (A 'dumb' Access Point) back to a centralized switch for QoS, firewalls, etc, etc, etc. It's a beautiful architecture and has a few VERY nice features such as; Multiple MAC addresses per Access Port which means that different VLANs from the same Access Port may have different BSSIDs (thus reducing power consumption on the client devices).

Orinoco – A LONG time runner in the wireless LAN arena, they've just realized a VERY feature rich AP4000 (a/b/g). I personally haven't played with it yet but it looks to support just about every standard you could hope for and even a couple that are still under development.

3Com – After what I would call "an initial failure to understand the wireless market", 3Com have redesigned their range and have begun to add a lot more functionality to integrate in with the rest of the network. I've been a long-time fan of 3Com equipment due to its high MTBF (Mean Time Between Failure) and its Access Points seem to be following the same path.