If you do a lot of heterologous protein expression, take a look at Eurogentec's CherryExpress Kit. Based on the T7 expression system, the CherryExpress vector has a sequence encoding a small red polypeptide (the heme binding part of cytochrome) fused to the promoter. When your favorite gene is cloned in, the resulting fusion protein is bright red, allowing easy identification of clones expressing your gene. Even better, protein expression level can be quantified at 480nm and the highly soluble peptide could even improve the soluble expression of your protein. Tasty.