I have an Asus P5B Deluxe mobo with wireless and an Intel Core2 Duo E6600 2.4ghz.
Have to take the computer in for a coupla enhancements and I was thinking of upgrading the CPU at the same time. I do a lot of photoshop work... However the tech told me to basically figure it out myself by checking Asus' website, that is, what CPU to use. Asus has some comments about beta next to some of the chips, so not sure. I don't want to have problems.
What would be compatible with my mobo in the $300 or so range?
DO NOT spend $300 on a CPU for that motherboard. LOL You're using the LGA 775 socket, which is now out of date (not obsolute, but old). New CPUs aren't being made for that socket anymore. It's now been replaced by 1156 & 1366 sockets (i5 & i7 CPUs).
A Core 2 Quad CPU would be a good upgrade if you use modern versions of Photoshop and other such programs, as they can use quad cores. Otherwise, something like an E8400 or E8500 would be very good dual-core chips.
You should be able to get into any of those for well under $200. Considering you can buy an i5-750 (GREAT CPU) for $199 (although you'd need new motherboard) it'd be a waste to spend more than $200 at this point.
You could also consider a good cooler for your E6600, and overclocking it. The E6600 should overclock to 3.2Ghz or more fairly easily as I recall.