Here are some databases for finding information on specific genes and SNPs (single nucleotide polymorphisms):
Atlas of Genetics and Cytogenetics in Oncology and Haematology: site with information on cancer genes
COSMIC: catalogue of mutations in cancer
ENSEMBL: collection of genome databases for several species
Genecards: database of human genes and genomic information
Genetics Home Reference: reference guide for specific genes
KEGG: database of molecular information
OMIM: database of human genes and genetic phenotypes
PharmGKB: database featuring pharmacogenomic data
SNPedia: wiki with information on variations in DNA
