I developed an interest in the Budapest fighting after seeing the scenario for Romanians fighting Hungarians in Budapest in the Eastern Front Scenarios book for the Rapid Fire gaming system.
I also bought 'Axis Allies on the Ostfront' by Bob Mackenzie which is a basically a TO&E guide for games where 1 vehicle or infantry stand equals a platoon (Spearhead, TAC, and Command Decision really). It contains a lot of info on the Hungarian garrison forces in Budapest.
The 'Stalin's Europe' supplement for Flames of War is full of lovely eye candy and some useful information. Personally I play FoW in both 15mm and 6mm scales and I have found the system to be a fairly reasonable representation of WW2 ground combat, if you don't 'power game'.
Another nice book on the Hungarian Front overall in 1944-45 is 'The Panzer's Last Stand' by Phillip Guillemot published by Histoire et Collections, number 8 in their Men and Battles series. It's a bit idiosyncratic in its translation into English but has loads of B&W photos, some lovely colour plates of AFVs and some pictures of re-enactors in genuine kit representing various units (mostly German) involved.
There is also an Osprey book with illustrations of Hungarian and Romanian troops but I do not have a copy, yet!