On first look, it seems that only a handful of some units (Katyushas, SPG's, some American-supplied equipment etc.) but troop numbers are fine (maybe a few more SMG and engineer stands just to be safe).
It's tanks where I've got the big gap. I need a load of later T-34's (B's and D's - the latter to include 85mm guns) as well as T-70's for later conflicts and T-26's / BT-7's for the earlier conflicts.
Trucks is also an area for additional work - I may chuck in some American trucks as the Russians liked them (unlike the tanks!). Some scenarios (I seem to remember) require the use of British and US tanks - which I'll then re-paint and use them to start an Allied army.
I also aim to buy a few ground attack aircraft (Sturmovich!).
So the shopping list for the birthday is almost complete! I think I need to spend another £40 but will have enough to play the Russians throughout the war. Which is nice.