Attic fans have been studied to death, and the benefit is marginal at best, and often negative. If it's a self-powered solar version and you have an excellent air seal between conditioned space & attic, studies at Texas A & M and the Florida Solar Energy Center say you can save as much as 6% in cooling electricity. See:
http://www.fsec.ucf.edu/en/publications/html/FSEC-GP-171-00/
But if you don't have a good air seal between conditioned space and the attic an attic fan can even INCREASE the power used, since it'll be pulling air-conditioned air in to the attic (cooling it nicely), from the living space below, which pulls in hot air from outside. (If you have non-air-tight recessed lights penetrating the attic floor, open plumbing chase, etc. an attic fan will have a net-negative performance.)
Radiant barriers have also been studied to death- they work, but with diminishing returns with increased R value in your insulation. The Oak Ridge National Lab has done a reasonable financial analysis placing a present-value on a 25 year return (the most you should pay to break even after 25 years) based on the location/climate, R-value of the insulation and whether you have ducts in the attic above the insulation or not. See:
http://www.ornl.gov/sci/roofs+walls/radiant/rb_tables.html#table4
So, looking at the table if you live in Phoenix and have R19 attic insulation, you should pay no more than $0.17/ft^2 if none of your ducts are in the attic, $0.23/ft^2 with ducts. If you have R38 up there, that drops to $0.12/ft^2 with ducts, $0.08/ft^2 without.
The values drop a bit if the RB is attached to the roof deck vs. under the rafters:
http://www.ornl.gov/sci/roofs+walls/radiant/rb_tables.html#table5
Most of the time additional insulation is a better deal:
http://www.ornl.gov/sci/roofs+walls/radiant/rb_tables.html#table6
Shingle temps will run hotter, but not 25F hotter (more like 10-15F). But the solar reflectance & infra-red emissivity of the roofing and the pitch of the roof makes a bigger difference in shingle temp than whether there's radiant-barrier below or not. Steeply pitched roofs convection cool from the the exterior nicely, whereas flat roofs stagnate at high temps, etc.
If the attic joists are exposed the joist-tops absorb radiated heat from the roof deck all too well, and the R-value of the joist is far lower than that of the insulation between them. Open-blow cellulose to cover the joist tops by 3" or more is usually a significant improvement in reducing the heat gain, since it puts ~R12 thermal break over the thermal-short circuit of the joist.
Fiberglass works for this too, but being slightly translucent to infra-red it passes some, and absorbs some in the upper few inches, making the layer of insulation an inch or two below the top the hottest place in the attic (significantly hotter than the ambient air.) You'll need 5.5" (R19) or more over the top to get the full effect or 3.75" high-density (R15) "cathedral ceiling batting. Cellulose absorbs the radiated heat a the surface then re-radiates the heat back to the attic rather than cooking from within, so in thin-layers it'll measurably outperform fiberglass. Above R25 or so the differences are inconsequential, and difficult or impossible to measure.
But from a fit point of view, blown insulations fill all the gaps & voids. At even modest insulation levels the gaps, thin spots and voids will dominate the heat gain, so making the fit as-perfect as possible with blown insulation is usually worth a ~15% performance improvement even at identical R-values.
If you only have R19 batting in the attic, a 6" overblow of cellulose that covers the joist tops & fills in the gaps will cut the heat-gain by more than half. A radiant barrier perfectly installed might net you a ~30% reduction (best case.) Above R40, even a very hot attic is unlikely to be your largest heat-gain. (South facing windows, even when shaded from direct get about 50% of the heat gain as they would in direct sun, primarily from scattered light. Exterior window shades/shutters take that down immensely. Shading exterior walls on the E, S, & W sides also makes measurable differences in the cooling load.)
If you're doing an insulation overblow, take the time to air-seal the space as well as you possibly can, foam sealing all electrical & plumbing penetrations, weather stripping the access doors/hatches, etc. Replacing recessed light fixtures with gasketed air-tight insulation-contact types is also advisable. Do NOT insulate over a fixture not rated for insulation contact, (even if you're using high-efficiency LED or compact fluorescent bulbs.) Building a fire-resistant air-tight box over them with 3" clearances can work, but it's time consuming- it must be installed in an air tight fashion to stop convection induced by a super-heated attic from pulling conditioned air up from the living space (adding to the cooling load.)
