If it is a small network i would use 3com. If it is mid-size i would go with hp, but i would consider Cisco before anything.  

It's almost 700 workstations split across 2 sites. Cisco is way too expensive.

We have users logging on and off every hour, so the data load is very high at these times. Once logged on we do have a lot of streaming demands but not constantly.

I am assuming this matches HP more than 3com?

Cisco would be your way to go, but between the two you have listed i would go HP all the way, i would make sure you incorporate layer 3 routing into this type of setup at your core.

If you have a lot of money and you want to look cool like everyone else, go with cisco. j/k I would stay away just because of costs alone.  It will cost more to have a worth while engineer that knows what theyre doing on cisco equip. Plus if you want firmware upgrades, you;; need to purchase smartnet.

I dont know about HP but 3com will give you a pretty big bang for the buck.  Most of thier enterprise line of routers and switches comes with a lifetime warranty and free firmware upgrades.  Training may not be as abundant but it will be much easier to manage and learn

Single-vendor for network devices is a very good idea.
 
On the other hand, I have used Cisco, HP & 3COM all in mixed LANs and I did very much like HP, although that was a generation of HP switches ago so I couldn't vouch for the latest ones.

I have used Avaya, 3COM, Enterasys (formerly Cabletron) Cisco, Nortel, and HP Procurve switches in different environments. Given my choice, I would choose Cisco, but if budget is an issue, I would recommend Enterasys for several reasons.  First they are a cheaper alternative to Cisco and they have a VERY similar command-line interface.  The GUI that you can use to manage the Enterasys switches is  called Netsight - and it is nice.  I work for a large company now that has an all Enterasys network (over 6000 Enterasys switches) and it is very stable.  We can easily manage them using Netsight and the switches cost A LOT less than Cisco.  The tech support is very good as well.

That's my recommendation.  I'd stay away from HP Procurve only because I have had my share of problems with the support - support has been slow and/or unable/unwilling to quickly resolve issues.

3COM is very good if that is what you have as an alternative (if you can't consider any other vendors).  One of my former employers had an all 3COM network for several years... in fact the core of their network had been all 3COM (same switches) for over 10 years when I got there.  Although I can't say that I support having the equipment installed for that long (obviously one should replace the equipment every few years) that still tells me that the equipment is very reliable.  What you get for your $ is a good product with really good support.

Hope that helps.

Not too biased, was it..  I have standardized on 3Com.  With my eyes wide open.  I know their performance is great and the price/performance is what puts them over the top for us. I know that Cisco has the best support, but its not worth paying twice the cost for it. (All you Cisco bigots out there, just chill... its true - unless Cisco finds themselves in a competitive sale and drops their pants to get the business... There are distinct marketing and sales patterns that you can pick up from Cisco reps if you pay attention.)  I have also used Netgear and have little complaints, but the 3Com just delivers more features/ updated software, and performance (again).  HP has a much better warranty than anybody.  Their stuff is good, but its sort of like vanilla ice cream for me.  Some of their port densities and features on a specific device  just doesnt match my needs.  The newer 3Com switches offer several price points in different family models (just like Cisco) and their joint venture with Huawei bears solid, well tested fruit before it hits the US. When you look at the global sales, they move more units than most other vendors.

  Ok, all you Crisco lovers, tear me to pieces!  I wanted to buy Cisco, but everytime I evaluate, I just cant do it. (when looking at price/ performance/ and ease of use)

Everything really boils down to how much money you want to spend, if your network is not requred to be high scale with high avalibility then 3com is the way to go. I always use the old saying "you get what you pay for" leads to the reason why Cisco cost more than that of a 3Com. while 3com is ok, it is not a Cisco.