I have a list of cDNA sequence ids (e.g., NM_005502.2). How can I get the corresponding Ensembl transcript id, i.e., ENSTXXXXXXXXX.
Biomart is the best and available in Ensembl's main page
A really cool ID mapping tool called The Synergizer from the Roth Laboratory might be helpful in this case. Alternatively, you could use BioMart to map your cDNA sequence IDs to ENSEMBL transcript IDs.
A short video about how to use BioMart to map identifiers is here: