unix commands

I know some basic unix things, but I know there's a lot more out there.  Anyone care to share some of the things you find useful?  I basically only use these commands so far(and pipes and subcommands with $): cd, ls, chmod, mkdir, rmdir, rm , mv, cp, cat, less, grep, wc, find.

some things I like so far:
"cat file | less" is pretty cool for instant file viewing
"grep anything" grep rocks

% cat /dev/urandom|perl
Unmatched [ in regex; marked by <-- HERE in m/ʸƤ·
                                                 ñ¿E
R½Rµ*Hͭ}1y:7çäT²oéì§j&¤Ýh° <-- HERE næÃÉ`ÎÕC¨»!(é¹ôÂI¶¦ûʲkÄu(R´Y!#B·U3Þ`¾hØ*Û6±Tüµõ_À­ ¾P +ÛOÝêõué#t Û*øî"g°5oþѷuªʋô×ChGDÀJҶÉ%9Nôæ~wICê./ at - line 2.

penraps@foxtrot:~$ cat /dev/urandom|bash
bash: line 1: $'\234\221': command not found
bash: line 7: $'\220k\353Ja.\252\301\237\366Y\327\240\327\006': command not found
bash: line 7: j@®×/f!à#×YëÚc Ò             BgIÌ..úùc6­[òQÔV§Zþ* Ê´ú÷ZÉ7ÚìÁCË«v<ËĪ/§U§¿{i§XPE·R}ï_õ³:¦o¨2¾ÔÀ¾Ê@ìagHîÜL/ÃUyé
     bash: line 7: $'8\2718\031IR\306\250\302\323\375\322\0314\374\340\a\303\001q': command not found
bash: line 7: $'\212\022}X{.z\306\304\2053{\252mU\334\334\307\373\333': command not found
bash: command substitution: line 8: unexpected EOF while looking for matching `"'
bash: command substitution: line 9: syntax error: unexpected end of file
bash: line 7: $'\002\327L\220\364\200\334\360\254MJ}F\327e\222\230\322\352a\344\347\023F\235+l\366\3652~Z\022s\202\310\252\335M\225': command not found
bash: command substitution: line 8: syntax error near unexpected token `)'
bash: command substitution: line 8: `»³û!~ßc ÷¦Ã{©ËbA¹Ä)9ãWsSD¢eC1ðÈÕG(qç¶Ás¶7ø'
bash: line 7: $'\363&\232Y\206\275\311\315\242+i2\305\275\351_\326:3\345\213\262\220\326mt\016\225a\241\'\006\371\310\315\316\236\3737\340f\336\302\301\306\025\277\350\215\E\264\377\330\312Z\340Ry\302\275\307f\224%V\216\360\275\330\205k\236\257\003\343\322\2507\274m\364\317\327\323\204\306\374\347]D\250\030-\307{\247\366\312wp\360\262M\210A\241\003\030Cx\225\032\366R\232\3752h\177\340O\332\234\333\317GP\362\242\341\211ZW\354\233\232\2528^\230o\004\031\247\340\342h}\205\245\223e1\212\335\225\302\277\374\211\261\236\215D:l\365B\241\343\347\336\257\337\30151\263\360\347\321\243\261\v9S\204\306\232\f\3103\265=\346\374\237\323\316\315#m\325\212\307,!\355[\211_\203\312\202\300\027dy\344Lb~\031\354e\375\243\336\205v\351WT@\305\200=\032\233\002\f<\016=\222\2247\231\200k\362\263': command not found
bash: line 8: $'\243\371@UA': command not found
bash: line 16: ©²ûwÿ
                    RB·==: No such file or directory
bash: line 18: jêNVêDäïyM¡: No such file or directory
bash: command substitution: line 19: unexpected EOF while looking for matching `''
bash: command substitution: line 20: syntax error: unexpected end of file
bash: command substitution: line 16: unexpected EOF while looking for matching `''
bash: command substitution: line 17: syntax error: unexpected end of file
bash: line 16: öC¸«CTíUSñÿÁ¦Q§IPgÚ=ÀvÏÉgÜKORÚÚB
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bash: line 17: ¬9úQ No such file or directoryQ¯§²q òa:^%Sú]ñÓ
bash: line 19: syntax error«ïU|zzysȬÚzn»ºk1D3:CN­i|>©õì"¢T*ëRóàµ×9®ã­Å]u/ªä9°Üx&uÅlbJ¼1=jçç<RZ¹Üw^laFgÊs:Å*Âf¡uGò>î"y'
penraps@foxtrot:~$

# cat /dev/urandom|bash
# exit
$ ls
$