insert into t values (seq.nextval, .....) 

select seq.nextval into idv from dual;
insert into t values (idv, ....)  

select seq.nextval into idv from dual;
insert into t values (idv, ....)  

insert into t 
select seq.nextval .... from dual;

insert into t values (seq.nextval, .....) 

select seq.nextval into idv from dual;
insert into t values (idv, ....)  

SQL> select * from v$version;

BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Prod
PL/SQL Release 10.2.0.1.0 - Production
CORE    10.2.0.1.0      Production
TNS for 32-bit Windows: Version 10.2.0.1.0 - Production
NLSRTL Version 10.2.0.1.0 - Production

SQL> create sequence sq1;

Sequence created.

SQL> create table t_seq (x int);

Table created.

SQL> insert into t_seq values(sq1.nextval);

1 row created.

Straight Sequences
When you had to use a sequence in a PL/SQL program earlier, you had to use a construct like SELECT <Seq>.NEXTVAL INTO <VariableName> FROM DUAL prior to this release.

declare
        trans_id number(10);
begin
        select myseq.nextval
        into trans_id
        from dual;
end;

Not anymore. You can directly assign the next value of a sequence to a variable: 
declare
        trans_id number(10);
begin
        trans_id := myseq.nextval;
end;
/

Now, that's what I call simplicity. 

SQL> select * from v$version;

BANNER
-----------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.1.0.6.0 - Production
PL/SQL Release 11.1.0.6.0 - Production
CORE    11.1.0.6.0      Production
TNS for Linux: Version 11.1.0.6.0 - Production
NLSRTL Version 11.1.0.6.0 - Production

SQL> create sequence dummy_seq;

Sequence created.

SQL> var x number
SQL> exec :x := dummy_seq.nextval

PL/SQL procedure successfully completed.

SQL> print x

         X
----------
         1

declare x int; begin x := dummy_seq.nextval; end;


call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.16          0          0          0           0
Execute      1      0.00       0.02          0          0          0           1
Fetch        0      0.00       0.00          0          0          0           0
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total        2      0.00       0.18          0          0          0           1

Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: 20  

Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  SQL*Net message to client                       1        0.00          0.00
  SQL*Net message from client                     1        0.01          0.01
********************************************************************************

Select DUMMY_SEQ.NEXTVAL 
from
 dual


call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.04          0          0          0           0
Execute      1      0.00       0.00          0          0          0           0
Fetch        1      0.00       0.00          0          0          0           1
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total        3      0.00       0.04          0          0          0           1