Problem: You have a dynamically linked binary with 
stripped symbols, How do you find where main() is loaded in memory?

Answer:
In gdb:

We will use /bin/ls as an example. The way the ELF
format works there is an absolute entry address. The
very start of execution does a bunch of initialization
and then lets the c run time takeover. The function
that starts this all is

libc_start_main

The first argument of this function is a function pointer
to main. 

libc_start_main( (int)(*func)(int argc, char *argv[], char **envp) func, ...);

So here is how you find the entry point:

(gdb) i file
Symbols from "/bin/ls".
Local exec file:
	`/bin/ls', file type elf32-i386.
	Entry point: 0x8049cd0

These are first instructions at the entry point:

(gdb) x/20i 0x8049cd0
0x8049cd0:	xor    %ebp,%ebp
0x8049cd2:	pop    %esi
0x8049cd3:	mov    %esp,%ecx
0x8049cd5:	and    $0xfffffff0,%esp
0x8049cd8:	push   %eax
0x8049cd9:	push   %esp
0x8049cda:	push   %edx
0x8049cdb:	push   $0x805bd20
0x8049ce0:	push   $0x805bd30
0x8049ce5:	push   %ecx
0x8049ce6:	push   %esi
0x8049ce7:	push   $0x804fb50
0x8049cec:	call   0x804980c <__libc_start_main@plt>
0x8049cf1:	hlt    
0x8049cf2:	nop
0x8049cf3:	nop
0x8049cf4:	nop


The c run time provides some functions for program initialization.
This starts with libc_start_main and sets up the heap, runs constructors
and destructors, and then calls the programs main function.

The format of libc_start_main can be seen above.

Here are the interesting parametsers, commented with ; comments

0x8049cd8:      push   %eax
0x8049cd9:      push   %esp
0x8049cda:      push   %edx
0x8049cdb:      push   $0x805bd20	; constructor code
0x8049ce0:      push   $0x805bd30	; destructor code
0x8049ce5:      push   %ecx
0x8049ce6:      push   %esi
0x8049ce7:      push   $0x804fb50       ; &main code
0x8049cec:      call   0x804980c <__libc_start_main@plt>

Final answer:
Main begins at 0x804fb50.