Immediatly after entering the beta?
bought Fallout's one and two, maybe second sight

So far I have bought :
Soldiers: Heroes of World War II
Original War
Lionheart: Legacy of the Crusader
Of course I know that I will be buying more.

I've bought Die By the Sword so far, simply because I think the devs deserve the money and I'd like more companies to try these open types of control systems (For the record, I already had the game burned to a CD just in case the game was truly lost in public memory or something). And frankly buying the real game off of ebay doesn't give the devs anything.
I plan on buying Fallout 1/2 /tactics, Kingpin, and Second Sight (Though i'd rather have Psi Ops), but haven't simply because that's alot to put on my gaming plate right now with Little Big Planet being released on October 21st.

First purchase was MDK, and then I used my free game voucher on its sequel.
I them opted for Die By The Sword (nevermind the fact that I already have a hard copy of this game, I wanted the expansion, not to mention wanting to verify if the installer works well or not for everyone else) and Hostile Waters afterward.
A day or two later, I decided to give Giants: Citizen Kabuto a shot, and was immediately hooked. (It also rekindled my interest in Armed and Dangerous, another third-person shooter from Planet Moon Studios that also has its fair share of hilarity.)
When the Redneck Rampage Collection released, I also immediately purchased that, mostly because while I had the original game, I didn't have Route 66 or Rides Again - Arkansas.
A few weeks later, I gave Sacrifice a chance, mostly because I wanted to learn about all the funny things like Bovine Intervention. It's one of the few RTSs I've actually shown much interest in due to the much more personal feel you get when you actually control someone on the battlefield.

1st, Redneck Rampage Collection
2nd, Second Sight
3rd, Fallout 1
4th, Fallout 2

purchased:
1. Fallout 1
2. Freespace 1
on my radar:
3. Fallout 2
4. Redneck Rampage

First purchase was Giants: Citizen Kabuto
Free voucher purchase: Sacrifice
Last purchase: Kingpin

First Purchase: Fallout 1
Free Game: Fallout 2
Next in line: Giants or Fallout Tactics... Can't decide which.

Purchased Fallout Tactics, got Fallout 1 free.

fallout 2

Giants: Citizen Kabuto
followed by Sacrifice with my freebie
Next in line are Fallout 1+2, MDK 1+2, Earthworm Jim 1+2 (do we see a pattern here?) and maybe some Descent.
I'm planning on getting these all at once as soon as the price of the dollar is more reasonable.

I got EWJ1+2, and I am not sure if I want to get Redneck Rampage or Kingpin next.

1st - fallout
freebie - fallout tactics
2nd - fallout 2
waiting for JA2:UB to be updated to 1.01 -- that'll be my next purchase.

Straight up:
Sacrifice
freebie: Descent 1&2
Messiah
After a little while:
MDK2
Earthworm 1&2
Fallout

Purchased
Fallout 1 (got Fallout 2 for free :))
Redneck Rampage
Looking at:
Giants: Citizen Kabuto
Waiting for:
System Shock 2