Well for starters, I would have preferred an AMD build for the budget build, with an X2 240\245 and an inexpensive motherboard like the GA-MA74GM-S2; it would provide for a better upgrade path IMO.
Also, I would have recommended the GA-MA770T-UD3P for the Entry-level Gaming Build; it is usually found as cheap as the MSI board on mWave, and Gigabyte boards are usually much more reliable than others (coming from personal experience). In addition, the Corsair 450VX is a better option for said build compared to the OCZ PSU; build quality is far better on the Corsair, and rebates are almost always available on Newegg that bring the price down below $50.
For the Mid-Range Build, I would prefer using OCZ XMP modules, since they provide the user with the option of running an XMP which makes the modules run at 1800MHz with a simple setting in the BIOS, while being only $10 or so more expensive than other modules. I would also have preferred going with the Sunbeam Transformer or NZXT Zero 2 full-tower cases instead of the mid-tower Antec Three Hundred.
And lastly, regarding the High-End Build, I would have gone with the Barracuda 7200.11 1.5TB drive instead of the WD Caviar Green, due to the significant speed advantage of the Barracuda drive over the WD drive. Also, I would have chosen a modular PSU like the 850HX; the extra $40 is worth it for this kind of system IMO.
That is a lot of nitpicks eh?
But hey, you asked for it!