The �celtic cross�

 

(With and without the white and black lining/fimbriation, both usual forms).

The celtic cross is probably the most popular symbol among (seemingly not only) european neonazis, even more than the traditional swastika (but that�s maybe because the swastika is banned or has its use �protected� in many countries). They base it in that Celts are �true� Europeans (i.e., of �pure� breed).
The circle/cross design has (like the swastika) a long and honourable usage before it was associated with modern nazism. The circle/cross is another variation of the solar disk, and is found in ancient American, Asian, and European cultures. It was also associated with Celtic Christianity. The symbol also has various meanings in alchemy and hermetic studies.
I suspect that the present users care less for the actual symbolism involved than they value its similarity to the swastika design, and substitute it for a swastika when such a design is illegal.

This white power cross is a popular symbol amongst Europe�s hardcore Nazis. It is molded after the Celtic cross, seeking to make an heritage issue of it.

Black celtic cross on white, as opposed to the more usual white celtic cross on black, used on european neo-nazi flags.

Odal rune

Another popular rune among neonazi organizations is the odal rune (notably the by the South african African Student Federation). It is the last letter of futhark, the �modern� 16 letter viking rune set. (Here with and without the white and black lining/fimbriation, both usual forms).

The odal was originally used by ethnic Germans (Volksdeutsche) from Yugoslavia SS-regiment (the 7. SS Freiwillingen-Gebirgs -- Division Prinz Eugen) operating during the WWII in the Nazi Germany sponsored State of Croatia. According to FlagMaster 073 [flm], it may have been used by ethnic Germans in other countries.
Another version (with arrows at the end) was used by the 23. SS-Freiwilligen-Panzer-Grenadier-Division "Nederland".

The werewolf symbol

I found a brief but interesting description of a symbol that appears on some current nazist flags: 

A fascist sign, used in for instance Sweden in the 1990s, meaning werewolf. According to ancient superstitions men were sometimes transformed into beings, half men, half wolves, extremely blood-thirsty and ferocious. These beings were called werewolves. Werwolf, German for "werewolves", was the name chosen for the guerilla fighters Hitler and the Nazi top had planned should continue the fight against the invading Allies when Germany�s Wehrmacht was defeated and the German territory was occupied.