How about a GGTS? MANY different battery combos and tube lengths based on your needs...
http://www.e-cigarette-wiki.com/index.php?title=GGTS&printable=yes
1 x 14500 3.7v for a total of 3.7v
1 x 14650 3.7v for a total of 3.7v
1 x CR2 3.7v for a total of 3.7v
1 x CR123A 3.7v for a total of 3.7v
1 x 16340 3.7v for a total of 3.7v
1 x 17340 3.7v for a total of 3.7v
1 x 17500 3.7v for a total of 3.7v
1 x 17670 3.7v for a total of 3.7v
1 x 18350 3.7v for a total of 3.7v
1 x 18500 3.7v for a total of 3.7v
1 x 18650 3.7v for a total of 3.7v
2 x 15270 3.0v for a total of 6.0v (High resistance atomizer required)
2 x CR123A 3.0v for a total of 6.0v (High resistance atomizer required)
2 x 16340 3.0v for a total of 6.0v (High resistance atomizer required)
2 x 17340 3.0v for a total of 6.0v (High resistance atomizer required)
2 x 14500 3.2v for a total of 6.4v (High resistance atomizer and extension sleeve required)
2 x 16340 3.2v for a total of 6.4v (High resistance atomizer required)
2 x 17340 3.2v for a total of 6.4v (High resistance atomizer required)
2 x 14500 3.6v for a total of 7.2v (High resistance atomizer and extension sleeve required)
2 x CR2 3.6v for a total of 7.2v (High resistance atomizer required)
2 x 16340 3.6v for a total of 7.2v (High resistance atomizer required)
2 x CR2 3.7v for a total of 7.4v (High resistance atomizer required)
2 x 14500 3.7v for a total of 7.4v (High resistance atomizer and extension sleeve required)
2 x 16340 3.7v for a total of 7.4v (High resistance atomizer required)
2 x 17280 3.7v for a total of 7.4v (High resistance atomizer required)
2 x 17340 3.7v for a total of 7.4v (High resistance atomizer required)
2 x CR123A 3.7v for a total of 7.2v (High resistance atomizer required)
2 x 18350 3.7v for a total of 7.4v (High resistance atomizer required)
2 x 18500 3.7v for a total of 7.4v (High resistance atomizer and extension sleeve required)
2 x 18650 3.7v for a total of 7.4v (High resistance atomizer and extension sleeve required)