Recomendation for cheap and best raspberry pi or equivalent

Hi, I am trying to build a "awesome pi server-router" for caching, proxy, webapp env(testing env), learning virtualisation, ap/router, and so many awesome learning insane ideas, i want to dive in with. So plese enlighten newbeie like me with the type of pi-dereviatives (pi,banana,humming,beagle) model number, any link routing to amazon or anything from your experiences.

One of my friend suggested me this: Beagle: http://goo.gl/W3MRfg

P.S. I am an arch-user, so if any archians like me out there, please some words of wisdom here.

Thank you for you help. Appreciated :)