There is a lot going on in Akihabara, so I've made up a map for you.
Finished Buildings
1. Akihabara Dai Building: 147.5 m, finished March 2005
2. Tokyo Times Tower: 138.45 m, finished September 2004
3. Akihabara UDX: 107.7 m, finished January 2006
4. Orix Akihabara Building: 81.15 m, finished October 2005
5. Yodobashi Akiba Building: 60 m, finished 2005
Under Construction
6. Fujisoft ABC Akihabara Building: 146.69, finished January 2007
7. Park Tower Akihabara: 80.7 m, maybe finished September 2006
8. Akihabara Zone 8 Building: 74.8 m, finished April 2007
9. TX Akihabara Station Front Building: 74.6, begun February 2006, no end date listed
Proposed
10. Akihabara Plan: 99.5 m, to begin March 2007, no end date listed
There are two buildings under construction close to the World Trade Center. There is Crest Forme Shiba Tower (クレストフォルム芝タワー) which is 136.4 m tall residential tower which should be finished in November of 2007. The other one is the Shiodome I-2 Block Office Complex Zone Redevelopment (汐留I-2街区業務系複合ゾーン開発計画) which is a 133.48 m tall office building to be completed in March of 2008.
You were probably thinking of Crest Forme Shiba Tower because it is quite tall now. The Shiodome Building is still only a few floors tall.