[Optsol]

It's the simplest (to start and to maintain) of self-employed retrirement options. It's just like opening an ira, but with an extra form (5305 -- IIRC).
All the usual suspects (brokerage houses, banks, etc...) offer them.

Aside from the SE aspects (potential large yearly contributions), and the extra form(one shot fill-out), they behave the same as a traditional ira.

Before you jump in though -- the core limitation is that the contribution is based on a % of your SE income, unlike traditional & roth.

Traditional & roth, if you make 3000, you can put in all 3000
SEP, if you net 3000, you can only put in 600 (=25% of your after-deducted earnings)

So if you are starting small, you may wish to stay with the conventional IRAs. When you get to the point where 25% of your after deducted net exceeds the traditional IRA limit, or if your total income limits your IRA contributions, then the SEP is for you.

If any of this isn't clear, please post, I'll try to improve it.