Mac Mini or equivalent

For the hardware geeks amongst us, I'm after some advice. :) I want a small computer to run Roll20 in a Hangout, as long as it does that I'll be happy. Ideally it will also run two screens. I've got my eyes on the Mac Mini (cuz I like Mac OS), however it is more expensive than some similar products, what's the minimum spec I would need to comfortably run the above? Thanks in advance.

I don't know about hangout or two screens, but I run roll20 with reasonably complex maps and plenty of minis on a Dell Mini 9, which is a bit being 'starting' to get flaky, but wouldn't exactly have been a powerhouse when new.  And I can do that while looking at facebook, or otherwise surfing the net, in the background, and having skype open and functional. So, if a 5 year old netbook can run it...  chances are reasonable that any computer you get now would be sufficient.

I've got a mac mini, and I can run roll20 pretty consistently. But my computer's got some problems, and it's four years old. I would say that honestly, osx is just about the only thing the mac mini's got going for it. From what I've been told, the hardware for the mac mini is basically just the parts from last year's laptops. That being said however, I am on my second mac mini. So they're not as bad as I may be making them out. If price is a concern though, I don't think "mac" anything should be in the running.

It really just depends on your preference for OS. You can find laptops on sale with celeron processors in the $300 USD range that can run roll20 no sweat. One thing I've personally seen with my for 2 quad and 430gt card, is that it works about the same as my tablet running a tegra 3 micro processor. The only time you'd really run into issues is multi tasking with a few programs. If you're not huge on technology, I'm pretty much saying a 9 year old computer could run roll20 no problem, as can ANY 2013 computer.

If you're looking for a cheap, small, and very quiet box that will do it you might consider a Chromebox. My Samsung Chromebook runs Roll20 and Hangouts fine, and the Chromebox has double the processing power. It's not a Windows or Mac device though, so it depends what else you want to do with this device.

The OP stated his preference for the mac OS and I was looking at the stats on the mac mini. If it is the same as he was talking about it lists as the following cpu : 2.5 I5 (dual core) or 2.3 gig I7 (quad core) HDD : 500 gig Graphics :  Intel HD Graphics 4000 Memory : 4 gigs of DDR3 memory. From what I could find and look over, it should run roll20 with little to no problem. I've ran the boards on a 2.2 single core amd with 3 gigs of DDR2 memory. The HDD size does come into play as it is mostly the cpu, memory, and graphics. The only thing I'm not sure on is the Graphics and that will need a mod or dev to answer that. The rest is plenty for running a game on this site.

Thanks everyone, dual monitors is more important than operating system

Most economy line desktops still offer dual monitor support. Anything with a sandy/ivy bridge Intel or A series AMD support it on a budget. You just have to look at the back of the computer to see if it has two video ports. One important thing is to MAKE sure that if it has two DVI ports(white)  that you have DVI (white) monitors, as many computers have shifted to digital only. (If it only has white video ports and HDMIs, it probably won't work with your blue port only monitors)

The other thing to take in account is that even in a dual monitor setup the players will see what the gm is looking at. If this is for players to see one thing while the gm is looking at another then it is a two computer setup not dual monitor.

Unless he has two different browsers (on on each monitor) and one is set to Player View...

true that is possible but he would have to share the mouse and keyboard also or do the rolls himself which is a strong possibility unless he is planning on just using it as a battlemat with token movement. That would eliminate the need of the second computer setup and run it like you suggest G.V.