If you’re trying to build a list, you need an autoresponder. Period.
Aweber is one of the oldest autoresponders on the web (if not the oldest). They have more experience in this game than just about anybody. Their service is solid.
I used Aweber for many years, and I still think it has the most intuitive interface – it’s super easy to use, and very powerful indeed.
Note: I now use Convert Fox as that comes with a full marketing suite but I still recommend Aweber highly.
If you’re looking for a low cost way to get started building your list, then I recommend Aweber.