[SQL] Most recent row

This question has been asked a few times, and Google returns a few different 
answers, but I am interested people's opinions and suggestions for the *best* 
wat to retrieve the most recent row from a table.

My case is:

create table people ( p_id  serial primary key,......
);

create table assessments ( p_id    int4 not null references people(p_id), as_timestamp    timestamp not null, ......
);

select p.*, (most recent) a.*  from people p, assessments a ..
;