If Apple were magically to buy back all my POS Macs to date and they were to pay for the OS X -> Windows application suite porting that is currently ongoing then disappear without a trace, I'd not only do a little dance of joy but stick with pretty much what I have - the equivalents being:
XServe -> HP Proliant / Dell Poweredge
Not that I'm extremely unhappy with the XServes all things considered, but I have more choice and more consistent support from HP/Dell.
Pro Pro -> HP xw8600 / Dell Precision T7400
The souped-up Toyota vans to Apple's Escalade. More stable and genuinely 'just works' in a wider variety of situations, supported for actually professional use, better engineered for a hard working life, more practically expandable and ultimately more powerful as a result.
Home Pro -> Above + Dell XPS 730 H2C - or a DIY for gaming
The Pro is not really a home enthusiast / entertainment fit. Windows offers far better choices instead of the amusing triumphal posts of "Look what I put into my Pro with extreme effort that anyone can do on a reasonably powerful PC in 5 minutes!".
Air -> Sony TT / UX
A gorgeous joke. The TT is not.
Alu Macbook -> Sony SZ / Z
The newest SZ I have which I didn't buy NOS is a year old - yet it's still a better machine than the Macbook for a 13-inch life on the road, although I'll concede that the Macbook is better looking (I like the sharp lines on the SZ too though). The Z on the other hand is not only more suitable for those looking towards the 15-inch MBP but actually spend a lot of time with a notebook instead of a DTR, but even the midrange models blows away the Macbook for not much more.
Macbook Pro 15-inch -> Sony Z / Dell XPS 16
I don't actually have a Windows 15-inch right now, but the Z and XPS excellently fill in the upper and lower end of the functions of such a machine. To me, despite its relative popularity the 15-inch size is a little compromised: Too small to be a DTR and too heavy to be an actual all-day mobile companion.
Macbook Pro 17-inch -> Dell Precision M6400 Covet
Because if you're going big, there's no point in going half-assed. I also find the orange quite refreshing.
iMac -> ???
Maybe a Touchsmart or an XPS One - or an XPS Studio. I picked the iMac as I thought even Apple couldn't screw up a machine that'll be used about three times a week in the kitchen. So far I've been right about both the iMacs in that role.
Mini
I don't have either Apple or Windows equivalents of this right now. But Dell's Studio Hybrid is a decent alternative, as is the Studio XPS if you have more room on your table.