Best bang-for-buck purchase you have made?

3-way tie, I think:
1) Dared SL1200A preamp (w/Mullard CV4024s & a Bendix 6106 rectifier), replaced a Sonic Frontiers SFL-1
2) KAB/Technics SL1200MK2 turntable that absolutely wiped the floor with my Michell TechnoDec/Audionote combo
3) $50 Chinese 6SN7-based USB DAC (listening to Pandora Radio with it right now, wonderful w/a pair of Raytheons!)

Eastern Electric Minimax Preamp
Gallo Nucleus Speakers
Mapleshade Speaker Jumpers

Benchmark DAC1 USB for my PC

Philips MFB 545 active speakers for 1200 usd, made in the early eighties. 3 ways speakers, three in-built amplifiers (75 watts, 50 watts, 25 watts) with 12 inch woofers. Lovely full bodied sound of the seventies, with a good dose of dynamism and speed. Actually, to hear a violin concerto on these speakers are revealing: there is an orchestra behind the violinist. No more hassle with speaker-amp-speaker cable-power cable matching. It works well with the supplied Chinese pcs (Although I have recently bought VH audio flavour 4 pcs.)There are bass and treble and volume controls, so I could adjust the sound to the quality of recordings (typically, when I play - very rarely - pop or rock music, I need to reduce bass level).

Home-made corner bass traps. Cost all of $40 for materials for two of them plus about 20mins to put them together. They do an excellent job cleaning up the bass frequencies. This "product" has given me by far the best improvement per dollar spent I have ever had.

In terms of buying something that someone else made, I would say that my Denon DL103R cart is pretty much the cat's pajamas.