Bones,
All Donationware has now been made freeware, so you can save your wallet on that one. As far as where to get the most bang for your buck, I would recommend Alphasim.
Some of their models have been made freeware, such as those found on this page...
http://www.alphasim.co.uk/as_freeware.html
The only trouble is they don't make a lot of models for CFS2 anymore. The one model I can recommend to you is the Fairey Swordfish. I have a weapons loadout for her that give you the same setup as the Groundcrew model. The airfile is more realistic...taking off with a torpedo or a spread of 250lb bombs is literally walking a tightrope...you have a 50/50 shot of hitting the water. Also, doing a torpedo run at 85 knots is extremely discomforting.
http://www.alphasim3.com/store/product_info.php?cPath=22&products_id=43
Their models are pricey, though...
As far as Icarus is concerned, I've found some of their stuff hit-or-miss. I like their Westland Lysander and the Fiat Br-20 Cicogna (which is useful for CAI / Chianti, the prop textures notwithstanding) I was less impressed with the Cr-32, and the Junkers Ju-86.
http://www.icarusgold.com/RAF.htm
We've also reached a saturation point where most of the aircraft choices (especially for WWII) have a quality freeware counterpart.
There are two excellent models from Sky Unlimited that can be converted...
http://www.skyunlimited.net/re2005.htm
http://www.skyunlimited.net/mig3_fs2004.htm
While the MiG-3 now has a comparable freeware counterpart, the Re-2005 does not.
And of course, there's always DamBusters...
http://www.justflight.com/product.asp?pid=66
I've already done Mustang Vs Fw-190 and Mosquito Squadron...plus Battle of Britain Memorial Flight and Pearl Harbor are severely outdated and not worth it.