I have a client who is leasing an industrial building with a local network. They are rapidly expanding and need additional space. The nearest available property is available across the street about 150 feet away door-to-door. Now obviously running an ethernet cable would be quite a feat. So I am wondering if there is any other way to connected without VPN or direct ethernet. Possibly a wireless solution? What devices do you recommend? Their current environment is Windows 2008 server with file sharing for about 15 clients and a DSL connection. When they plan to move, they will be upgrading to a T1, Exchange server, and also VoIP phones.
150 feet is not that far. For the money, versus speed, I would bury conduit with fiber in it.
It might cost a few thousand to have this professionally done, but this is a business, and the cost of doing business would dictate spending the money you need to do the job the best way.
Consider that a VPN with their DSL upload speeds, or T-1, are both going to be roughly 1.5 Mbps (T-1) to maybe 2 Mbps (for a typical DSL). You will still probably have to spend money on the firewalls to connect them (at least on the second one), and a second Internet connection. In the long run, you will also be paying more by having to pay for that second connection every month over the long haul. This option stinks.
Then your other option: Wireless. it is still much slower, for good equipment it costs a lot more than $200 as in the other answer (VERY bad answer, IMO), still much slower than a fiber connection, and it is not as stable as the underground method. Heavy rain, or other factors will interfere with it. You will find this to be a major pain in the butt, and they will not be happy in the long run.
Seriously, any other answer than fiber here, is probably going to get you fired (I see you are a consultant by your website) when someone, who knows what they are doing, eventually questions it.
I did not need the links below to tell you this, but do not just take my opinion on this. In each case below, they are talking much greater distances even.
Any bridge you can attach a directional antenna to should work, provided you have reasonable line of sight. A wireless router that supports OpenWRT and/or DD-WRT and has detachable antennas is a cheap way to do it (under $200). Products like http://www.ubnt.com/nanobridge seem promising too, as there's already a directional antenna and suitable housing for outdoor use.